Release: 2.0.26 | Release Date: February 11, 2024

# SQLAlchemy 2.0 Documentation

# Session API

## Session and sessionmaker()

Object Name | Description
--- | ---
ORMExecuteState | Represents a call to the `Session.execute()` method, as passed to the `SessionEvents.do_orm_execute()` event hook.
Session | Manages persistence operations for ORM-mapped objects.
sessionmaker | A configurable `Session` factory.
SessionTransaction | A `Session`-level transaction.
SessionTransactionOrigin | indicates the origin of a `SessionTransaction`.

class sqlalchemy.orm.sessionmaker

  A configurable `Session` factory.

  The `sessionmaker` factory generates new `Session` objects when called, creating them given the configurational arguments established here.

  e.g.:

      from sqlalchemy import create_engine
      from sqlalchemy.orm import sessionmaker

      # an Engine, which the Session will use for connection
      # resources
      engine = create_engine('postgresql+psycopg2://scott:tiger@localhost/')

      Session = sessionmaker(engine)

      with Session() as session:
          session.add(some_object)
          session.add(some_other_object)
          session.commit()

  Context manager use is optional; otherwise, the returned `Session` object may be closed explicitly via the `Session.close()` method. Using a `try:/finally:` block is optional, however will ensure that the close takes place even if there are database errors:

      session = Session()
      try:
          session.add(some_object)
          session.add(some_other_object)
          session.commit()
      finally:
          session.close()

  `sessionmaker` acts as a factory for `Session` objects in the same way as an `Engine` acts as a factory for `Connection` objects. In this way it also includes a `sessionmaker.begin()` method, that provides a context manager which both begins and commits a transaction, as well as closes out the `Session` when complete, rolling back the transaction if any errors occur:

      Session = sessionmaker(engine)

      with Session.begin() as session:
          session.add(some_object)
          session.add(some_other_object)
      # commits transaction, closes session

  New in version 1.4.

  When calling upon `sessionmaker` to construct a `Session`, keyword arguments may also be passed to the method; these arguments will override that of the globally configured parameters. Below we use a `sessionmaker` bound to a certain `Engine` to produce a `Session` that is instead bound to a specific `Connection` procured from that engine:

      Session = sessionmaker(engine)

      # bind an individual session to a connection

      with engine.connect() as connection:
          with Session(bind=connection) as session:
              # work with session

  The class also includes a method `sessionmaker.configure()`, which can be used to specify additional keyword arguments to the factory, which will take effect for subsequent `Session` objects generated. This is usually used to associate one or more `Engine` objects with an existing `sessionmaker` factory before it is first used:

      # application starts, sessionmaker does not have
      # an engine bound yet
      Session = sessionmaker()

      # ... later, when an engine URL is read from a configuration
      # file or other events allow the engine to be created
      engine = create_engine('sqlite:///foo.db')
      Session.configure(bind=engine)

      sess = Session()
      # work with session

  See also

  Opening and Closing a Session - introductory text on creating sessions using `sessionmaker`.

  Members

  __call__(), __init__(), begin(), close_all(), configure(), identity_key(), object_session()

  Class signature

  class `sqlalchemy.orm.sessionmaker` (`sqlalchemy.orm.session._SessionClassMethods`, `typing.Generic`)

  method `sqlalchemy.orm.sessionmaker.` __call__(**local_kw: Any) → _S

    Produce a new `Session` object using the configuration established in this `sessionmaker`.

    In Python, the `__call__` method is invoked on an object when it is “called” in the same way as a function:

        Session = sessionmaker(some_engine)
        session = Session()  # invokes sessionmaker.__call__()

  method `sqlalchemy.orm.sessionmaker.` __init__(bind: Optional[_SessionBind] = None, *, class_: Type[_S] = <class 'sqlalchemy.orm.session.Session'>, autoflush: bool = True, expire_on_commit: bool = True, info: Optional[_InfoType] = None, **kw: Any)

    Construct a new `sessionmaker`.

    All arguments here except for `class_` correspond to arguments accepted by `Session` directly. See the `Session.__init__()` docstring for more details on parameters.

    Parameters:

      - bind – a `Engine` or other `Connectable` with which newly created `Session` objects will be associated.

      - class_ – class to use in order to create new `Session` objects. Defaults to `Session`.

      - autoflush –

        The autoflush setting to use with newly created `Session` objects.

        See also

        Flushing - additional background on autoflush

      - expire_on_commit=True – the `Session.expire_on_commit` setting to use with newly created `Session` objects.

      - info – optional dictionary of information that will be available via `Session.info`. Note this dictionary is updated, not replaced, when the `info` parameter is specified to the specific `Session` construction operation.

      - **kw – all other keyword arguments are passed to the constructor of newly created `Session` objects.

  method `sqlalchemy.orm.sessionmaker.` begin() → AbstractContextManager[_S]

    Produce a context manager that both provides a new `Session` as well as a transaction that commits.

    e.g.:

        Session = sessionmaker(some_engine)

        with Session.begin() as session:
            session.add(some_object)

        # commits transaction, closes session

    New in version 1.4.

  classmethod `sqlalchemy.orm.sessionmaker.` close_all() → None

    inherited from the `sqlalchemy.orm.session._SessionClassMethods.close_all` method of `sqlalchemy.orm.session._SessionClassMethods`

    Close all sessions in memory.

    Deprecated since version 1.3: The `Session.close_all()` method is deprecated and will be removed in a future release. Please refer to `close_all_sessions()`.

  method `sqlalchemy.orm.sessionmaker.` configure(**new_kw: Any) → None

    (Re)configure the arguments for this sessionmaker.

    e.g.:

        Session = sessionmaker()

        Session.configure(bind=create_engine('sqlite://'))

  classmethod `sqlalchemy.orm.sessionmaker.` identity_key(class_: Type[Any] | None = None, ident: Any | Tuple [Any, ...] = None, *, instance: Any | None = None, row: Row [Any] | RowMapping | None = None, identity_token: Any | None = None) → _IdentityKeyType[Any]

    inherited from the `sqlalchemy.orm.session._SessionClassMethods.identity_key` method of `sqlalchemy.orm.session._SessionClassMethods`

    Return an identity key.

    This is an alias of `identity_key()`.

  classmethod `sqlalchemy.orm.sessionmaker.` object_session(instance: object) → Session | None

    inherited from the `sqlalchemy.orm.session._SessionClassMethods.object_session` method of `sqlalchemy.orm.session._SessionClassMethods`

    Return the `Session` to which an object belongs.

    This is an alias of `object_session()`.

class sqlalchemy.orm.ORMExecuteState

  Represents a call to the `Session.execute()` method, as passed to the `SessionEvents.do_orm_execute()` event hook.

  New in version 1.4.

  See also

  Execute Events - top level documentation on how to use `SessionEvents.do_orm_execute()`

  Members

  __init__(), all_mappers, bind_arguments, bind_mapper, execution_options, invoke_statement(), is_column_load, is_delete, is_executemany, is_insert, is_orm_statement, is_relationship_load, is_select, is_update, lazy_loaded_from, load_options, loader_strategy_path, local_execution_options, parameters, session, statement, update_delete_options, update_execution_options(), user_defined_options

  Class signature

  class `sqlalchemy.orm.ORMExecuteState` (`sqlalchemy.util.langhelpers.MemoizedSlots`)

  method `sqlalchemy.orm.ORMExecuteState.` __init__(session: Session, statement: Executable, parameters: _CoreAnyExecuteParams | None, execution_options: _ExecuteOptions, bind_arguments: _BindArguments, compile_state_cls: Type[ORMCompileState] | None, events_todo: List[_InstanceLevelDispatch[ Session ]])

    Construct a new `ORMExecuteState`.

    this object is constructed internally.

  attribute `sqlalchemy.orm.ORMExecuteState.` all_mappers

    Return a sequence of all `Mapper` objects that are involved at the top level of this statement.

    By “top level” we mean those `Mapper` objects that would be represented in the result set rows for a `select()` query, or for a `update()` or `delete()` query, the mapper that is the main subject of the UPDATE or DELETE.

    New in version 1.4.0b2.

    See also

    `ORMExecuteState.bind_mapper`

  attribute `sqlalchemy.orm.ORMExecuteState.` bind_arguments: _BindArguments

    The dictionary passed as the `Session.execute.bind_arguments` dictionary.

    This dictionary may be used by extensions to `Session` to pass arguments that will assist in determining amongst a set of database connections which one should be used to invoke this statement.

  attribute `sqlalchemy.orm.ORMExecuteState.` bind_mapper

    Return the `Mapper` that is the primary “bind” mapper.

    For an `ORMExecuteState` object invoking an ORM statement, that is, the `ORMExecuteState.is_orm_statement` attribute is `True`, this attribute will return the `Mapper` that is considered to be the “primary” mapper of the statement. The term “bind mapper” refers to the fact that a `Session` object may be “bound” to multiple `Engine` objects keyed to mapped classes, and the “bind mapper” determines which of those `Engine` objects would be selected.

    For a statement that is invoked against a single mapped class, `ORMExecuteState.bind_mapper` is intended to be a reliable way of getting this mapper.

    New in version 1.4.0b2.

    See also

    `ORMExecuteState.all_mappers`

  attribute `sqlalchemy.orm.ORMExecuteState.` execution_options: _ExecuteOptions

    The complete dictionary of current execution options.

    This is a merge of the statement level options with the locally passed execution options.

    See also

    `ORMExecuteState.local_execution_options`

    `Executable.execution_options()`

    ORM Execution Options

  method `sqlalchemy.orm.ORMExecuteState.` invoke_statement(statement: Executable | None = None, params: _CoreAnyExecuteParams | None = None, execution_options: OrmExecuteOptionsParameter | None = None, bind_arguments: _BindArguments | None = None) → Result [Any]

    Execute the statement represented by this `ORMExecuteState`, without re-invoking events that have already proceeded.

    This method essentially performs a re-entrant execution of the current statement for which the `SessionEvents.do_orm_execute()` event is being currently invoked. The use case for this is for event handlers that want to override how the ultimate `Result` object is returned, such as for schemes that retrieve results from an offline cache or which concatenate results from multiple executions.

    When the `Result` object is returned by the actual handler function within `SessionEvents.do_orm_execute()` and is propagated to the calling `Session.execute()` method, the remainder of the `Session.execute()` method is preempted and the `Result` object is returned to the caller of `Session.execute()` immediately.

    Parameters:

      - statement – optional statement to be invoked, in place of the statement currently represented by `ORMExecuteState.statement`.

      - params –

        optional dictionary of parameters or list of parameters which will be merged into the existing `ORMExecuteState.parameters` of this `ORMExecuteState`.

        Changed in version 2.0: a list of parameter dictionaries is accepted for executemany executions.

      - execution_options – optional dictionary of execution options will be merged into the existing `ORMExecuteState.execution_options` of this `ORMExecuteState`.

      - bind_arguments – optional dictionary of bind_arguments which will be merged amongst the current `ORMExecuteState.bind_arguments` of this `ORMExecuteState`.

    Returns:

      a `Result` object with ORM-level results.

    See also

    Re-Executing Statements - background and examples on the appropriate usage of `ORMExecuteState.invoke_statement()`.

  attribute `sqlalchemy.orm.ORMExecuteState.` is_column_load

    Return True if the operation is refreshing column-oriented attributes on an existing ORM object.

    This occurs during operations such as `Session.refresh()`, as well as when an attribute deferred by `defer()` is being loaded, or an attribute that was expired either directly by `Session.expire()` or via a commit operation is being loaded.

    Handlers will very likely not want to add any options to queries when such an operation is occurring as the query should be a straight primary key fetch which should not have any additional WHERE criteria, and loader options travelling with the instance will have already been added to the query.

    New in version 1.4.0b2.

    See also

    `ORMExecuteState.is_relationship_load`

  attribute `sqlalchemy.orm.ORMExecuteState.` is_delete

    return True if this is a DELETE operation.

  attribute `sqlalchemy.orm.ORMExecuteState.` is_executemany

    return True if the parameters are a multi-element list of dictionaries with more than one dictionary.

    New in version 2.0.

  attribute `sqlalchemy.orm.ORMExecuteState.` is_insert

    return True if this is an INSERT operation.

  attribute `sqlalchemy.orm.ORMExecuteState.` is_orm_statement

    return True if the operation is an ORM statement.

    This indicates that the select(), insert(), update(), or delete() being invoked contains ORM entities as subjects. For a statement that does not have ORM entities and instead refers only to `Table` metadata, it is invoked as a Core SQL statement and no ORM-level automation takes place.

  attribute `sqlalchemy.orm.ORMExecuteState.` is_relationship_load

    Return True if this load is loading objects on behalf of a relationship.

    This means, the loader in effect is either a LazyLoader, SelectInLoader, SubqueryLoader, or similar, and the entire SELECT statement being emitted is on behalf of a relationship load.

    Handlers will very likely not want to add any options to queries when such an operation is occurring, as loader options are already capable of being propagated to relationship loaders and should be already present.

    See also

    `ORMExecuteState.is_column_load`

  attribute `sqlalchemy.orm.ORMExecuteState.` is_select

    return True if this is a SELECT operation.

  attribute `sqlalchemy.orm.ORMExecuteState.` is_update

    return True if this is an UPDATE operation.

  attribute `sqlalchemy.orm.ORMExecuteState.` lazy_loaded_from

    An `InstanceState` that is using this statement execution for a lazy load operation.

    The primary rationale for this attribute is to support the horizontal sharding extension, where it is available within specific query execution time hooks created by this extension. To that end, the attribute is only intended to be meaningful at query execution time, and importantly not any time prior to that, including query compilation time.

  attribute `sqlalchemy.orm.ORMExecuteState.` load_options

    Return the load_options that will be used for this execution.

  attribute `sqlalchemy.orm.ORMExecuteState.` loader_strategy_path

    Return the `PathRegistry` for the current load path.

    This object represents the “path” in a query along relationships when a particular object or collection is being loaded.

  attribute `sqlalchemy.orm.ORMExecuteState.` local_execution_options: _ExecuteOptions

    Dictionary view of the execution options passed to the `Session.execute()` method.

    This does not include options that may be associated with the statement being invoked.

    See also

    `ORMExecuteState.execution_options`

  attribute `sqlalchemy.orm.ORMExecuteState.` parameters: _CoreAnyExecuteParams | None

    Dictionary of parameters that was passed to `Session.execute()`.

  attribute `sqlalchemy.orm.ORMExecuteState.` session: Session

    The `Session` in use.

  attribute `sqlalchemy.orm.ORMExecuteState.` statement: Executable

    The SQL statement being invoked.

    For an ORM selection as would be retrieved from `Query`, this is an instance of `select` that was generated from the ORM query.

  attribute `sqlalchemy.orm.ORMExecuteState.` update_delete_options

    Return the update_delete_options that will be used for this execution.

  method `sqlalchemy.orm.ORMExecuteState.` update_execution_options(**opts: Any) → None

    Update the local execution options with new values.

  attribute `sqlalchemy.orm.ORMExecuteState.` user_defined_options

    The sequence of `UserDefinedOptions` that have been associated with the statement being invoked.

class sqlalchemy.orm.Session

  Manages persistence operations for ORM-mapped objects.

  The `Session` is not safe for use in concurrent threads.. See Is the Session thread-safe? Is AsyncSession safe to share in concurrent tasks? for background.

  The Session’s usage paradigm is described at Using the Session.

  Members

  __init__(), add(), add_all(), begin(), begin_nested(), bind_mapper(), bind_table(), bulk_insert_mappings(), bulk_save_objects(), bulk_update_mappings(), close(), close_all(), commit(), connection(), delete(), deleted, dirty, enable_relationship_loading(), execute(), expire(), expire_all(), expunge(), expunge_all(), flush(), get(), get_bind(), get_nested_transaction(), get_one(), get_transaction(), identity_key(), identity_map, in_nested_transaction(), in_transaction(), info, invalidate(), is_active, is_modified(), merge(), new, no_autoflush, object_session(), prepare(), query(), refresh(), reset(), rollback(), scalar(), scalars()

  Class signature

  class `sqlalchemy.orm.Session` (`sqlalchemy.orm.session._SessionClassMethods`, `sqlalchemy.event.registry.EventTarget`)

  method `sqlalchemy.orm.Session.` __init__(bind: _SessionBind | None = None, *, autoflush: bool = True, future: Literal[True] = True, expire_on_commit: bool = True, autobegin: bool = True, twophase: bool = False, binds: Dict[_SessionBindKey, _SessionBind] | None = None, enable_baked_queries: bool = True, info: _InfoType | None = None, query_cls: Type[ Query [Any]] | None = None, autocommit: Literal[False] = False, join_transaction_mode: JoinTransactionMode = 'conditional_savepoint', close_resets_only: bool | _NoArg = _NoArg.NO_ARG)

    Construct a new `Session`.

    See also the `sessionmaker` function which is used to generate a `Session`-producing callable with a given set of arguments.

    Parameters:

      - autoflush –

        When `True`, all query operations will issue a `Session.flush()` call to this `Session` before proceeding. This is a convenience feature so that `Session.flush()` need not be called repeatedly in order for database queries to retrieve results.

        See also

        Flushing - additional background on autoflush

      - autobegin –

        Automatically start transactions (i.e. equivalent to invoking `Session.begin()`) when database access is requested by an operation. Defaults to `True`. Set to `False` to prevent a `Session` from implicitly beginning transactions after construction, as well as after any of the `Session.rollback()`, `Session.commit()`, or `Session.close()` methods are called.

        New in version 2.0.

        See also

        Disabling Autobegin to Prevent Implicit Transactions

      - bind – An optional `Engine` or `Connection` to which this `Session` should be bound. When specified, all SQL operations performed by this session will execute via this connectable.

      - binds –

        A dictionary which may specify any number of `Engine` or `Connection` objects as the source of connectivity for SQL operations on a per-entity basis. The keys of the dictionary consist of any series of mapped classes, arbitrary Python classes that are bases for mapped classes, `Table` objects and `Mapper` objects. The values of the dictionary are then instances of `Engine` or less commonly `Connection` objects. Operations which proceed relative to a particular mapped class will consult this dictionary for the closest matching entity in order to determine which `Engine` should be used for a particular SQL operation. The complete heuristics for resolution are described at `Session.get_bind()`. Usage looks like:

            Session = sessionmaker(binds={
                SomeMappedClass: create_engine('postgresql+psycopg2://engine1'),
                SomeDeclarativeBase: create_engine('postgresql+psycopg2://engine2'),
                some_mapper: create_engine('postgresql+psycopg2://engine3'),
                some_table: create_engine('postgresql+psycopg2://engine4'),
                })

        See also

        Partitioning Strategies (e.g. multiple database backends per Session)

        `Session.bind_mapper()`

        `Session.bind_table()`

        `Session.get_bind()`

      - class_ – Specify an alternate class other than `sqlalchemy.orm.session.Session` which should be used by the returned class. This is the only argument that is local to the `sessionmaker` function, and is not sent directly to the constructor for `Session`.

      - enable_baked_queries –

        legacy; defaults to `True`. A parameter consumed by the `sqlalchemy.ext.baked` extension to determine if “baked queries” should be cached, as is the normal operation of this extension. When set to `False`, caching as used by this particular extension is disabled.

        Changed in version 1.4: The `sqlalchemy.ext.baked` extension is legacy and is not used by any of SQLAlchemy’s internals. This flag therefore only affects applications that are making explicit use of this extension within their own code.

      - expire_on_commit –

        Defaults to `True`. When `True`, all instances will be fully expired after each `commit()`, so that all attribute/object access subsequent to a completed transaction will load from the most recent database state.

        > See also

        > Committing

      - future –

        Deprecated; this flag is always True.

        See also

        SQLAlchemy 2.0 - Major Migration Guide

      - info – optional dictionary of arbitrary data to be associated with this `Session`. Is available via the `Session.info` attribute. Note the dictionary is copied at construction time so that modifications to the per- `Session` dictionary will be local to that `Session`.

      - query_cls – Class which should be used to create new Query objects, as returned by the `Session.query()` method. Defaults to `Query`.

      - twophase – When `True`, all transactions will be started as a “two phase” transaction, i.e. using the “two phase” semantics of the database in use along with an XID. During a `commit()`, after `flush()` has been issued for all attached databases, the `TwoPhaseTransaction.prepare()` method on each database’s `TwoPhaseTransaction` will be called. This allows each database to roll back the entire transaction, before each transaction is committed.

      - autocommit – the “autocommit” keyword is present for backwards compatibility but must remain at its default value of `False`.

      - join_transaction_mode –

        Describes the transactional behavior to take when a given bind is a `Connection` that has already begun a transaction outside the scope of this `Session`; in other words the `Connection.in_transaction()` method returns True.

        The following behaviors only take effect when the `Session` actually makes use of the connection given; that is, a method such as `Session.execute()`, `Session.connection()`, etc. are actually invoked:

        - `"conditional_savepoint"` - this is the default. if the given `Connection` is begun within a transaction but does not have a SAVEPOINT, then `"rollback_only"` is used. If the `Connection` is additionally within a SAVEPOINT, in other words `Connection.in_nested_transaction()` method returns True, then `"create_savepoint"` is used.

          `"conditional_savepoint"` behavior attempts to make use of savepoints in order to keep the state of the existing transaction unchanged, but only if there is already a savepoint in progress; otherwise, it is not assumed that the backend in use has adequate support for SAVEPOINT, as availability of this feature varies. `"conditional_savepoint"` also seeks to establish approximate backwards compatibility with previous `Session` behavior, for applications that are not setting a specific mode. It is recommended that one of the explicit settings be used.

        - `"create_savepoint"` - the `Session` will use `Connection.begin_nested()` in all cases to create its own transaction. This transaction by its nature rides “on top” of any existing transaction that’s opened on the given `Connection`; if the underlying database and the driver in use has full, non-broken support for SAVEPOINT, the external transaction will remain unaffected throughout the lifespan of the `Session`.

          The `"create_savepoint"` mode is the most useful for integrating a `Session` into a test suite where an externally initiated transaction should remain unaffected; however, it relies on proper SAVEPOINT support from the underlying driver and database.

          Tip

          When using SQLite, the SQLite driver included through Python 3.11 does not handle SAVEPOINTs correctly in all cases without workarounds. See the sections Serializable isolation / Savepoints / Transactional DDL and Serializable isolation / Savepoints / Transactional DDL (asyncio version) for details on current workarounds.

        - `"control_fully"` - the `Session` will take control of the given transaction as its own; `Session.commit()` will call `.commit()` on the transaction, `Session.rollback()` will call `.rollback()` on the transaction, `Session.close()` will call `.rollback` on the transaction.

          Tip

          This mode of use is equivalent to how SQLAlchemy 1.4 would handle a `Connection` given with an existing SAVEPOINT (i.e. `Connection.begin_nested()`); the `Session` would take full control of the existing SAVEPOINT.

        - `"rollback_only"` - the `Session` will take control of the given transaction for `.rollback()` calls only; `.commit()` calls will not be propagated to the given transaction. `.close()` calls will have no effect on the given transaction.

          Tip

          This mode of use is equivalent to how SQLAlchemy 1.4 would handle a `Connection` given with an existing regular database transaction (i.e. `Connection.begin()`); the `Session` would propagate `Session.rollback()` calls to the underlying transaction, but not `Session.commit()` or `Session.close()` calls.

        New in version 2.0.0rc1.

      - close_resets_only –

        Defaults to `True`. Determines if the session should reset itself after calling `.close()` or should pass in a no longer usable state, disabling re-use.

        New in version 2.0.22: added flag `close_resets_only`. A future SQLAlchemy version may change the default value of this flag to `False`.

        See also

        Closing - Detail on the semantics of `Session.close()` and `Session.reset()`.

  method `sqlalchemy.orm.Session.` add(instance: object, _warn: bool = True) → None

    Place an object into this `Session`.

    Objects that are in the transient state when passed to the `Session.add()` method will move to the pending state, until the next flush, at which point they will move to the persistent state.

    Objects that are in the detached state when passed to the `Session.add()` method will move to the persistent state directly.

    If the transaction used by the `Session` is rolled back, objects which were transient when they were passed to `Session.add()` will be moved back to the transient state, and will no longer be present within this `Session`.

    See also

    `Session.add_all()`

    Adding New or Existing Items - at Basics of Using a Session

  method `sqlalchemy.orm.Session.` add_all(instances: Iterable[object]) → None

    Add the given collection of instances to this `Session`.

    See the documentation for `Session.add()` for a general behavioral description.

    See also

    `Session.add()`

    Adding New or Existing Items - at Basics of Using a Session

  method `sqlalchemy.orm.Session.` begin(nested: bool = False) → SessionTransaction

    Begin a transaction, or nested transaction, on this `Session`, if one is not already begun.

    The `Session` object features autobegin behavior, so that normally it is not necessary to call the `Session.begin()` method explicitly. However, it may be used in order to control the scope of when the transactional state is begun.

    When used to begin the outermost transaction, an error is raised if this `Session` is already inside of a transaction.

    Parameters:

      nested – if True, begins a SAVEPOINT transaction and is equivalent to calling `Session.begin_nested()`. For documentation on SAVEPOINT transactions, please see Using SAVEPOINT.

    Returns:

      the `SessionTransaction` object. Note that `SessionTransaction` acts as a Python context manager, allowing `Session.begin()` to be used in a “with” block. See Explicit Begin for an example.

    See also

    Auto Begin

    Managing Transactions

    `Session.begin_nested()`

  method `sqlalchemy.orm.Session.` begin_nested() → SessionTransaction

    Begin a “nested” transaction on this Session, e.g. SAVEPOINT.

    The target database(s) and associated drivers must support SQL SAVEPOINT for this method to function correctly.

    For documentation on SAVEPOINT transactions, please see Using SAVEPOINT.

    Returns:

      the `SessionTransaction` object. Note that `SessionTransaction` acts as a context manager, allowing `Session.begin_nested()` to be used in a “with” block. See Using SAVEPOINT for a usage example.

    See also

    Using SAVEPOINT

    Serializable isolation / Savepoints / Transactional DDL - special workarounds required with the SQLite driver in order for SAVEPOINT to work correctly. For asyncio use cases, see the section Serializable isolation / Savepoints / Transactional DDL (asyncio version).

  method `sqlalchemy.orm.Session.` bind_mapper(mapper: _EntityBindKey[_O], bind: _SessionBind) → None

    Associate a `Mapper` or arbitrary Python class with a “bind”, e.g. an `Engine` or `Connection`.

    The given entity is added to a lookup used by the `Session.get_bind()` method.

    Parameters:

      - mapper – a `Mapper` object, or an instance of a mapped class, or any Python class that is the base of a set of mapped classes.

      - bind – an `Engine` or `Connection` object.

    See also

    Partitioning Strategies (e.g. multiple database backends per Session)

    `Session.binds`

    `Session.bind_table()`

  method `sqlalchemy.orm.Session.` bind_table(table: TableClause, bind: Engine | Connection ) → None

    Associate a `Table` with a “bind”, e.g. an `Engine` or `Connection`.

    The given `Table` is added to a lookup used by the `Session.get_bind()` method.

    Parameters:

      - table – a `Table` object, which is typically the target of an ORM mapping, or is present within a selectable that is mapped.

      - bind – an `Engine` or `Connection` object.

    See also

    Partitioning Strategies (e.g. multiple database backends per Session)

    `Session.binds`

    `Session.bind_mapper()`

  method `sqlalchemy.orm.Session.` bulk_insert_mappings(mapper: Mapper [Any], mappings: Iterable[Dict[str, Any]], return_defaults: bool = False, render_nulls: bool = False) → None

    Perform a bulk insert of the given list of mapping dictionaries.

    Legacy Feature

    This method is a legacy feature as of the 2.0 series of SQLAlchemy. For modern bulk INSERT and UPDATE, see the sections ORM Bulk INSERT Statements and ORM Bulk UPDATE by Primary Key. The 2.0 API shares implementation details with this method and adds new features as well.

    Parameters:

      - mapper – a mapped class, or the actual `Mapper` object, representing the single kind of object represented within the mapping list.

      - mappings – a sequence of dictionaries, each one containing the state of the mapped row to be inserted, in terms of the attribute names on the mapped class. If the mapping refers to multiple tables, such as a joined-inheritance mapping, each dictionary must contain all keys to be populated into all tables.

      - return_defaults –

        when True, the INSERT process will be altered to ensure that newly generated primary key values will be fetched. The rationale for this parameter is typically to enable Joined Table Inheritance mappings to be bulk inserted.

        Note

        for backends that don’t support RETURNING, the `Session.bulk_insert_mappings.return_defaults` parameter can significantly decrease performance as INSERT statements can no longer be batched. See “Insert Many Values” Behavior for INSERT statements for background on which backends are affected.

      - render_nulls –

        When True, a value of `None` will result in a NULL value being included in the INSERT statement, rather than the column being omitted from the INSERT. This allows all the rows being INSERTed to have the identical set of columns which allows the full set of rows to be batched to the DBAPI. Normally, each column-set that contains a different combination of NULL values than the previous row must omit a different series of columns from the rendered INSERT statement, which means it must be emitted as a separate statement. By passing this flag, the full set of rows are guaranteed to be batchable into one batch; the cost however is that server-side defaults which are invoked by an omitted column will be skipped, so care must be taken to ensure that these are not necessary.

        Warning

        When this flag is set, server side default SQL values will not be invoked for those columns that are inserted as NULL; the NULL value will be sent explicitly. Care must be taken to ensure that no server-side default functions need to be invoked for the operation as a whole.

    See also

    ORM-Enabled INSERT, UPDATE, and DELETE statements

    `Session.bulk_save_objects()`

    `Session.bulk_update_mappings()`

  method `sqlalchemy.orm.Session.` bulk_save_objects(objects: Iterable[object], return_defaults: bool = False, update_changed_only: bool = True, preserve_order: bool = True) → None

    Perform a bulk save of the given list of objects.

    Legacy Feature

    This method is a legacy feature as of the 2.0 series of SQLAlchemy. For modern bulk INSERT and UPDATE, see the sections ORM Bulk INSERT Statements and ORM Bulk UPDATE by Primary Key.

    For general INSERT and UPDATE of existing ORM mapped objects, prefer standard unit of work data management patterns, introduced in the SQLAlchemy Unified Tutorial at Data Manipulation with the ORM. SQLAlchemy 2.0 now uses “Insert Many Values” Behavior for INSERT statements with modern dialects which solves previous issues of bulk INSERT slowness.

    Parameters:

      - objects –

        a sequence of mapped object instances. The mapped objects are persisted as is, and are not associated with the `Session` afterwards.

        For each object, whether the object is sent as an INSERT or an UPDATE is dependent on the same rules used by the `Session` in traditional operation; if the object has the `InstanceState.key` attribute set, then the object is assumed to be “detached” and will result in an UPDATE. Otherwise, an INSERT is used.

        In the case of an UPDATE, statements are grouped based on which attributes have changed, and are thus to be the subject of each SET clause. If `update_changed_only` is False, then all attributes present within each object are applied to the UPDATE statement, which may help in allowing the statements to be grouped together into a larger executemany(), and will also reduce the overhead of checking history on attributes.

      - return_defaults – when True, rows that are missing values which generate defaults, namely integer primary key defaults and sequences, will be inserted one at a time, so that the primary key value is available. In particular this will allow joined-inheritance and other multi-table mappings to insert correctly without the need to provide primary key values ahead of time; however, `Session.bulk_save_objects.return_defaults` greatly reduces the performance gains of the method overall. It is strongly advised to please use the standard `Session.add_all()` approach.

      - update_changed_only – when True, UPDATE statements are rendered based on those attributes in each state that have logged changes. When False, all attributes present are rendered into the SET clause with the exception of primary key attributes.

      - preserve_order – when True, the order of inserts and updates matches exactly the order in which the objects are given. When False, common types of objects are grouped into inserts and updates, to allow for more batching opportunities.

    See also

    ORM-Enabled INSERT, UPDATE, and DELETE statements

    `Session.bulk_insert_mappings()`

    `Session.bulk_update_mappings()`

  method `sqlalchemy.orm.Session.` bulk_update_mappings(mapper: Mapper [Any], mappings: Iterable[Dict[str, Any]]) → None

    Perform a bulk update of the given list of mapping dictionaries.

    Legacy Feature

    This method is a legacy feature as of the 2.0 series of SQLAlchemy. For modern bulk INSERT and UPDATE, see the sections ORM Bulk INSERT Statements and ORM Bulk UPDATE by Primary Key. The 2.0 API shares implementation details with this method and adds new features as well.

    Parameters:

      - mapper – a mapped class, or the actual `Mapper` object, representing the single kind of object represented within the mapping list.

      - mappings – a sequence of dictionaries, each one containing the state of the mapped row to be updated, in terms of the attribute names on the mapped class. If the mapping refers to multiple tables, such as a joined-inheritance mapping, each dictionary may contain keys corresponding to all tables. All those keys which are present and are not part of the primary key are applied to the SET clause of the UPDATE statement; the primary key values, which are required, are applied to the WHERE clause.

    See also

    ORM-Enabled INSERT, UPDATE, and DELETE statements

    `Session.bulk_insert_mappings()`

    `Session.bulk_save_objects()`

  method `sqlalchemy.orm.Session.` close() → None

    Close out the transactional resources and ORM objects used by this `Session`.

    This expunges all ORM objects associated with this `Session`, ends any transaction in progress and releases any `Connection` objects which this `Session` itself has checked out from associated `Engine` objects. The operation then leaves the `Session` in a state which it may be used again.

    Tip

    In the default running mode the `Session.close()` method does not prevent the Session from being used again. The `Session` itself does not actually have a distinct “closed” state; it merely means the `Session` will release all database connections and ORM objects.

    Setting the parameter `Session.close_resets_only` to `False` will instead make the `close` final, meaning that any further action on the session will be forbidden.

    Changed in version 1.4: The `Session.close()` method does not immediately create a new `SessionTransaction` object; instead, the new `SessionTransaction` is created only if the `Session` is used again for a database operation.

    See also

    Closing - detail on the semantics of `Session.close()` and `Session.reset()`.

    `Session.reset()` - a similar method that behaves like `close()` with the parameter `Session.close_resets_only` set to `True`.

  classmethod `sqlalchemy.orm.Session.` close_all() → None

    inherited from the `sqlalchemy.orm.session._SessionClassMethods.close_all` method of `sqlalchemy.orm.session._SessionClassMethods`

    Close all sessions in memory.

    Deprecated since version 1.3: The `Session.close_all()` method is deprecated and will be removed in a future release. Please refer to `close_all_sessions()`.

  method `sqlalchemy.orm.Session.` commit() → None

    Flush pending changes and commit the current transaction.

    When the COMMIT operation is complete, all objects are fully expired, erasing their internal contents, which will be automatically re-loaded when the objects are next accessed. In the interim, these objects are in an expired state and will not function if they are detached from the `Session`. Additionally, this re-load operation is not supported when using asyncio-oriented APIs. The `Session.expire_on_commit` parameter may be used to disable this behavior.

    When there is no transaction in place for the `Session`, indicating that no operations were invoked on this `Session` since the previous call to `Session.commit()`, the method will begin and commit an internal-only “logical” transaction, that does not normally affect the database unless pending flush changes were detected, but will still invoke event handlers and object expiration rules.

    The outermost database transaction is committed unconditionally, automatically releasing any SAVEPOINTs in effect.

    See also

    Committing

    Managing Transactions

    Preventing Implicit IO when Using AsyncSession

  method `sqlalchemy.orm.Session.` connection(bind_arguments: _BindArguments | None = None, execution_options: CoreExecuteOptionsParameter | None = None) → Connection

    Return a `Connection` object corresponding to this `Session` object’s transactional state.

    Either the `Connection` corresponding to the current transaction is returned, or if no transaction is in progress, a new one is begun and the `Connection` returned (note that no transactional state is established with the DBAPI until the first SQL statement is emitted).

    Ambiguity in multi-bind or unbound `Session` objects can be resolved through any of the optional keyword arguments. This ultimately makes usage of the `get_bind()` method for resolution.

    Parameters:

      - bind_arguments – dictionary of bind arguments. May include “mapper”, “bind”, “clause”, other custom arguments that are passed to `Session.get_bind()`.

      - execution_options –

        a dictionary of execution options that will be passed to `Connection.execution_options()`, when the connection is first procured only. If the connection is already present within the `Session`, a warning is emitted and the arguments are ignored.

        See also

        Setting Transaction Isolation Levels / DBAPI AUTOCOMMIT

  method `sqlalchemy.orm.Session.` delete(instance: object) → None

    Mark an instance as deleted.

    The object is assumed to be either persistent or detached when passed; after the method is called, the object will remain in the persistent state until the next flush proceeds. During this time, the object will also be a member of the `Session.deleted` collection.

    When the next flush proceeds, the object will move to the deleted state, indicating a `DELETE` statement was emitted for its row within the current transaction. When the transaction is successfully committed, the deleted object is moved to the detached state and is no longer present within this `Session`.

    See also

    Deleting - at Basics of Using a Session

  attribute `sqlalchemy.orm.Session.` deleted

    The set of all instances marked as ‘deleted’ within this `Session`

  attribute `sqlalchemy.orm.Session.` dirty

    The set of all persistent instances considered dirty.

    E.g.:

        some_mapped_object in session.dirty

    Instances are considered dirty when they were modified but not deleted.

    Note that this ‘dirty’ calculation is ‘optimistic’; most attribute-setting or collection modification operations will mark an instance as ‘dirty’ and place it in this set, even if there is no net change to the attribute’s value. At flush time, the value of each attribute is compared to its previously saved value, and if there’s no net change, no SQL operation will occur (this is a more expensive operation so it’s only done at flush time).

    To check if an instance has actionable net changes to its attributes, use the `Session.is_modified()` method.

  method `sqlalchemy.orm.Session.` enable_relationship_loading(obj: object) → None

    Associate an object with this `Session` for related object loading.

    Warning

    `enable_relationship_loading()` exists to serve special use cases and is not recommended for general use.

    Accesses of attributes mapped with `relationship()` will attempt to load a value from the database using this `Session` as the source of connectivity. The values will be loaded based on foreign key and primary key values present on this object - if not present, then those relationships will be unavailable.

    The object will be attached to this session, but will not participate in any persistence operations; its state for almost all purposes will remain either “transient” or “detached”, except for the case of relationship loading.

    Also note that backrefs will often not work as expected. Altering a relationship-bound attribute on the target object may not fire off a backref event, if the effective value is what was already loaded from a foreign-key-holding value.

    The `Session.enable_relationship_loading()` method is similar to the `load_on_pending` flag on `relationship()`. Unlike that flag, `Session.enable_relationship_loading()` allows an object to remain transient while still being able to load related items.

    To make a transient object associated with a `Session` via `Session.enable_relationship_loading()` pending, add it to the `Session` using `Session.add()` normally. If the object instead represents an existing identity in the database, it should be merged using `Session.merge()`.

    `Session.enable_relationship_loading()` does not improve behavior when the ORM is used normally - object references should be constructed at the object level, not at the foreign key level, so that they are present in an ordinary way before flush() proceeds. This method is not intended for general use.

    See also

    `relationship.load_on_pending` - this flag allows per-relationship loading of many-to-ones on items that are pending.

    `make_transient_to_detached()` - allows for an object to be added to a `Session` without SQL emitted, which then will unexpire attributes on access.

  method `sqlalchemy.orm.Session.` execute(statement: Executable, params: _CoreAnyExecuteParams | None = None, *, execution_options: OrmExecuteOptionsParameter = {}, bind_arguments: _BindArguments | None = None, _parent_execute_state: Any | None = None, _add_event: Any | None = None) → Result [Any]

    Execute a SQL expression construct.

    Returns a `Result` object representing results of the statement execution.

    E.g.:

        from sqlalchemy import select
        result = session.execute(
            select(User).where(User.id == 5)
        )

    The API contract of `Session.execute()` is similar to that of `Connection.execute()`, the 2.0 style version of `Connection`.

    Changed in version 1.4: the `Session.execute()` method is now the primary point of ORM statement execution when using 2.0 style ORM usage.

    Parameters:

      - statement – An executable statement (i.e. an `Executable` expression such as `select()`).

      - params – Optional dictionary, or list of dictionaries, containing bound parameter values. If a single dictionary, single-row execution occurs; if a list of dictionaries, an “executemany” will be invoked. The keys in each dictionary must correspond to parameter names present in the statement.

      - execution_options –

        optional dictionary of execution options, which will be associated with the statement execution. This dictionary can provide a subset of the options that are accepted by `Connection.execution_options()`, and may also provide additional options understood only in an ORM context.

        See also

        ORM Execution Options - ORM-specific execution options

      - bind_arguments – dictionary of additional arguments to determine the bind. May include “mapper”, “bind”, or other custom arguments. Contents of this dictionary are passed to the `Session.get_bind()` method.

    Returns:

      a `Result` object.

  method `sqlalchemy.orm.Session.` expire(instance: object, attribute_names: Iterable[str] | None = None) → None

    Expire the attributes on an instance.

    Marks the attributes of an instance as out of date. When an expired attribute is next accessed, a query will be issued to the `Session` object’s current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction.

    To expire all objects in the `Session` simultaneously, use `Session.expire_all()`.

    The `Session` object’s default behavior is to expire all state whenever the `Session.rollback()` or `Session.commit()` methods are called, so that new state can be loaded for the new transaction. For this reason, calling `Session.expire()` only makes sense for the specific case that a non-ORM SQL statement was emitted in the current transaction.

    Parameters:

      - instance – The instance to be refreshed.

      - attribute_names – optional list of string attribute names indicating a subset of attributes to be expired.

    See also

    Refreshing / Expiring - introductory material

    `Session.expire()`

    `Session.refresh()`

    `Query.populate_existing()`

  method `sqlalchemy.orm.Session.` expire_all() → None

    Expires all persistent instances within this Session.

    When any attributes on a persistent instance is next accessed, a query will be issued using the `Session` object’s current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction.

    To expire individual objects and individual attributes on those objects, use `Session.expire()`.

    The `Session` object’s default behavior is to expire all state whenever the `Session.rollback()` or `Session.commit()` methods are called, so that new state can be loaded for the new transaction. For this reason, calling `Session.expire_all()` is not usually needed, assuming the transaction is isolated.

    See also

    Refreshing / Expiring - introductory material

    `Session.expire()`

    `Session.refresh()`

    `Query.populate_existing()`

  method `sqlalchemy.orm.Session.` expunge(instance: object) → None

    Remove the instance from this `Session`.

    This will free all internal references to the instance. Cascading will be applied according to the expunge cascade rule.

  method `sqlalchemy.orm.Session.` expunge_all() → None

    Remove all object instances from this `Session`.

    This is equivalent to calling `expunge(obj)` on all objects in this `Session`.

  method `sqlalchemy.orm.Session.` flush(objects: Sequence[Any] | None = None) → None

    Flush all the object changes to the database.

    Writes out all pending object creations, deletions and modifications to the database as INSERTs, DELETEs, UPDATEs, etc. Operations are automatically ordered by the Session’s unit of work dependency solver.

    Database operations will be issued in the current transactional context and do not affect the state of the transaction, unless an error occurs, in which case the entire transaction is rolled back. You may flush() as often as you like within a transaction to move changes from Python to the database’s transaction buffer.

    Parameters:

      objects –

      Optional; restricts the flush operation to operate only on elements that are in the given collection.

      This feature is for an extremely narrow set of use cases where particular objects may need to be operated upon before the full flush() occurs. It is not intended for general use.

  method `sqlalchemy.orm.Session.` get(entity: _EntityBindKey[_O], ident: _PKIdentityArgument, *, options: Sequence [ORMOption] | None = None, populate_existing: bool = False, with_for_update: ForUpdateParameter = None, identity_token: Any | None = None, execution_options: OrmExecuteOptionsParameter = {}, bind_arguments: _BindArguments | None = None) → _O | None

    Return an instance based on the given primary key identifier, or `None` if not found.

    E.g.:

        my_user = session.get(User, 5)

        some_object = session.get(VersionedFoo, (5, 10))

        some_object = session.get(
            VersionedFoo,
            {"id": 5, "version_id": 10}
        )

    New in version 1.4: Added `Session.get()`, which is moved from the now legacy `Query.get()` method.

    `Session.get()` is special in that it provides direct access to the identity map of the `Session`. If the given primary key identifier is present in the local identity map, the object is returned directly from this collection and no SQL is emitted, unless the object has been marked fully expired. If not present, a SELECT is performed in order to locate the object.

    `Session.get()` also will perform a check if the object is present in the identity map and marked as expired - a SELECT is emitted to refresh the object as well as to ensure that the row is still present. If not, `ObjectDeletedError` is raised.

    Parameters:

      - entity – a mapped class or `Mapper` indicating the type of entity to be loaded.

      - ident –

        A scalar, tuple, or dictionary representing the primary key. For a composite (e.g. multiple column) primary key, a tuple or dictionary should be passed.

        For a single-column primary key, the scalar calling form is typically the most expedient. If the primary key of a row is the value “5”, the call looks like:

            my_object = session.get(SomeClass, 5)

        The tuple form contains primary key values typically in the order in which they correspond to the mapped `Table` object’s primary key columns, or if the `Mapper.primary_key` configuration parameter were used, in the order used for that parameter. For example, if the primary key of a row is represented by the integer digits “5, 10” the call would look like:

            my_object = session.get(SomeClass, (5, 10))

        The dictionary form should include as keys the mapped attribute names corresponding to each element of the primary key. If the mapped class has the attributes `id`, `version_id` as the attributes which store the object’s primary key value, the call would look like:

            my_object = session.get(SomeClass, {"id": 5, "version_id": 10})

      - options – optional sequence of loader options which will be applied to the query, if one is emitted.

      - populate_existing – causes the method to unconditionally emit a SQL query and refresh the object with the newly loaded data, regardless of whether or not the object is already present.

      - with_for_update – optional boolean `True` indicating FOR UPDATE should be used, or may be a dictionary containing flags to indicate a more specific set of FOR UPDATE flags for the SELECT; flags should match the parameters of `Query.with_for_update()`. Supersedes the `Session.refresh.lockmode` parameter.

      - execution_options –

        optional dictionary of execution options, which will be associated with the query execution if one is emitted. This dictionary can provide a subset of the options that are accepted by `Connection.execution_options()`, and may also provide additional options understood only in an ORM context.

        New in version 1.4.29.

        See also

        ORM Execution Options - ORM-specific execution options

      - bind_arguments –

        dictionary of additional arguments to determine the bind. May include “mapper”, “bind”, or other custom arguments. Contents of this dictionary are passed to the `Session.get_bind()` method.

    Returns:

      The object instance, or `None`.

  method `sqlalchemy.orm.Session.` get_bind(mapper: _EntityBindKey[_O] | None = None, *, clause: ClauseElement | None = None, bind: _SessionBind | None = None, _sa_skip_events: bool | None = None, _sa_skip_for_implicit_returning: bool = False, **kw: Any) → Engine | Connection

    Return a “bind” to which this `Session` is bound.

    The “bind” is usually an instance of `Engine`, except in the case where the `Session` has been explicitly bound directly to a `Connection`.

    For a multiply-bound or unbound `Session`, the `mapper` or `clause` arguments are used to determine the appropriate bind to return.

    Note that the “mapper” argument is usually present when `Session.get_bind()` is called via an ORM operation such as a `Session.query()`, each individual INSERT/UPDATE/DELETE operation within a `Session.flush()`, call, etc.

    The order of resolution is:

    1. if mapper given and `Session.binds` is present, locate a bind based first on the mapper in use, then on the mapped class in use, then on any base classes that are present in the `__mro__` of the mapped class, from more specific superclasses to more general.

    2. if clause given and `Session.binds` is present, locate a bind based on `Table` objects found in the given clause present in `Session.binds`.

    3. if `Session.binds` is present, return that.

    4. if clause given, attempt to return a bind linked to the `MetaData` ultimately associated with the clause.

    5. if mapper given, attempt to return a bind linked to the `MetaData` ultimately associated with the `Table` or other selectable to which the mapper is mapped.

    6. No bind can be found, `UnboundExecutionError` is raised.

    Note that the `Session.get_bind()` method can be overridden on a user-defined subclass of `Session` to provide any kind of bind resolution scheme. See the example at Custom Vertical Partitioning.

    Parameters:

      - mapper – Optional mapped class or corresponding `Mapper` instance. The bind can be derived from a `Mapper` first by consulting the “binds” map associated with this `Session`, and secondly by consulting the `MetaData` associated with the `Table` to which the `Mapper` is mapped for a bind.

      - clause – A `ClauseElement` (i.e. `select()`, `text()`, etc.). If the `mapper` argument is not present or could not produce a bind, the given expression construct will be searched for a bound element, typically a `Table` associated with bound `MetaData`.

    See also

    Partitioning Strategies (e.g. multiple database backends per Session)

    `Session.binds`

    `Session.bind_mapper()`

    `Session.bind_table()`

  method `sqlalchemy.orm.Session.` get_nested_transaction() → SessionTransaction | None

    Return the current nested transaction in progress, if any.

    New in version 1.4.

  method `sqlalchemy.orm.Session.` get_one(entity: _EntityBindKey[_O], ident: _PKIdentityArgument, *, options: Sequence [ORMOption] | None = None, populate_existing: bool = False, with_for_update: ForUpdateParameter = None, identity_token: Any | None = None, execution_options: OrmExecuteOptionsParameter = {}, bind_arguments: _BindArguments | None = None) → _O

    Return exactly one instance based on the given primary key identifier, or raise an exception if not found.

    Raises `sqlalchemy.orm.exc.NoResultFound` if the query selects no rows.

    For a detailed documentation of the arguments see the method `Session.get()`.

    New in version 2.0.22.

    Returns:

      The object instance.

    See also

    `Session.get()` - equivalent method that instead

      returns `None` if no row was found with the provided primary key

  method `sqlalchemy.orm.Session.` get_transaction() → SessionTransaction | None

    Return the current root transaction in progress, if any.

    New in version 1.4.

  classmethod `sqlalchemy.orm.Session.` identity_key(class_: Type[Any] | None = None, ident: Any | Tuple [Any, ...] = None, *, instance: Any | None = None, row: Row [Any] | RowMapping | None = None, identity_token: Any | None = None) → _IdentityKeyType[Any]

    inherited from the `sqlalchemy.orm.session._SessionClassMethods.identity_key` method of `sqlalchemy.orm.session._SessionClassMethods`

    Return an identity key.

    This is an alias of `identity_key()`.

  attribute `sqlalchemy.orm.Session.` identity_map: IdentityMap

    A mapping of object identities to objects themselves.

    Iterating through `Session.identity_map.values()` provides access to the full set of persistent objects (i.e., those that have row identity) currently in the session.

    See also

    `identity_key()` - helper function to produce the keys used in this dictionary.

  method `sqlalchemy.orm.Session.` in_nested_transaction() → bool

    Return True if this `Session` has begun a nested transaction, e.g. SAVEPOINT.

    New in version 1.4.

  method `sqlalchemy.orm.Session.` in_transaction() → bool

    Return True if this `Session` has begun a transaction.

    New in version 1.4.

    See also

    `Session.is_active`

  attribute `sqlalchemy.orm.Session.` info

    A user-modifiable dictionary.

    The initial value of this dictionary can be populated using the `info` argument to the `Session` constructor or `sessionmaker` constructor or factory methods. The dictionary here is always local to this `Session` and can be modified independently of all other `Session` objects.

  method `sqlalchemy.orm.Session.` invalidate() → None

    Close this Session, using connection invalidation.

    This is a variant of `Session.close()` that will additionally ensure that the `Connection.invalidate()` method will be called on each `Connection` object that is currently in use for a transaction (typically there is only one connection unless the `Session` is used with multiple engines).

    This can be called when the database is known to be in a state where the connections are no longer safe to be used.

    Below illustrates a scenario when using gevent, which can produce `Timeout` exceptions that may mean the underlying connection should be discarded:

        import gevent

        try:
            sess = Session()
            sess.add(User())
            sess.commit()
        except gevent.Timeout:
            sess.invalidate()
            raise
        except:
            sess.rollback()
            raise

    The method additionally does everything that `Session.close()` does, including that all ORM objects are expunged.

  attribute `sqlalchemy.orm.Session.` is_active

    True if this `Session` not in “partial rollback” state.

    Changed in version 1.4: The `Session` no longer begins a new transaction immediately, so this attribute will be False when the `Session` is first instantiated.

    “partial rollback” state typically indicates that the flush process of the `Session` has failed, and that the `Session.rollback()` method must be emitted in order to fully roll back the transaction.

    If this `Session` is not in a transaction at all, the `Session` will autobegin when it is first used, so in this case `Session.is_active` will return True.

    Otherwise, if this `Session` is within a transaction, and that transaction has not been rolled back internally, the `Session.is_active` will also return True.

    See also

    “This Session’s transaction has been rolled back due to a previous exception during flush.” (or similar)

    `Session.in_transaction()`

  method `sqlalchemy.orm.Session.` is_modified(instance: object, include_collections: bool = True) → bool

    Return `True` if the given instance has locally modified attributes.

    This method retrieves the history for each instrumented attribute on the instance and performs a comparison of the current value to its previously committed value, if any.

    It is in effect a more expensive and accurate version of checking for the given instance in the `Session.dirty` collection; a full test for each attribute’s net “dirty” status is performed.

    E.g.:

        return session.is_modified(someobject)

    A few caveats to this method apply:

    - Instances present in the `Session.dirty` collection may report `False` when tested with this method. This is because the object may have received change events via attribute mutation, thus placing it in `Session.dirty`, but ultimately the state is the same as that loaded from the database, resulting in no net change here.

    - Scalar attributes may not have recorded the previously set value when a new value was applied, if the attribute was not loaded, or was expired, at the time the new value was received - in these cases, the attribute is assumed to have a change, even if there is ultimately no net change against its database value. SQLAlchemy in most cases does not need the “old” value when a set event occurs, so it skips the expense of a SQL call if the old value isn’t present, based on the assumption that an UPDATE of the scalar value is usually needed, and in those few cases where it isn’t, is less expensive on average than issuing a defensive SELECT.

      The “old” value is fetched unconditionally upon set only if the attribute container has the `active_history` flag set to `True`. This flag is set typically for primary key attributes and scalar object references that are not a simple many-to-one. To set this flag for any arbitrary mapped column, use the `active_history` argument with `column_property()`.

    Parameters:

      - instance – mapped instance to be tested for pending changes.

      - include_collections – Indicates if multivalued collections should be included in the operation. Setting this to `False` is a way to detect only local-column based properties (i.e. scalar columns or many-to-one foreign keys) that would result in an UPDATE for this instance upon flush.

  method `sqlalchemy.orm.Session.` merge(instance: _O, *, load: bool = True, options: Sequence [ORMOption] | None = None) → _O

    Copy the state of a given instance into a corresponding instance within this `Session`.

    `Session.merge()` examines the primary key attributes of the source instance, and attempts to reconcile it with an instance of the same primary key in the session. If not found locally, it attempts to load the object from the database based on primary key, and if none can be located, creates a new instance. The state of each attribute on the source instance is then copied to the target instance. The resulting target instance is then returned by the method; the original source instance is left unmodified, and un-associated with the `Session` if not already.

    This operation cascades to associated instances if the association is mapped with `cascade="merge"`.

    See Merging for a detailed discussion of merging.

    Parameters:

      - instance – Instance to be merged.

      - load –

        Boolean, when False, `merge()` switches into a “high performance” mode which causes it to forego emitting history events as well as all database access. This flag is used for cases such as transferring graphs of objects into a `Session` from a second level cache, or to transfer just-loaded objects into the `Session` owned by a worker thread or process without re-querying the database.

        The `load=False` use case adds the caveat that the given object has to be in a “clean” state, that is, has no pending changes to be flushed - even if the incoming object is detached from any `Session`. This is so that when the merge operation populates local attributes and cascades to related objects and collections, the values can be “stamped” onto the target object as is, without generating any history or attribute events, and without the need to reconcile the incoming data with any existing related objects or collections that might not be loaded. The resulting objects from `load=False` are always produced as “clean”, so it is only appropriate that the given objects should be “clean” as well, else this suggests a mis-use of the method.

      - options –

        optional sequence of loader options which will be applied to the `Session.get()` method when the merge operation loads the existing version of the object from the database.

        New in version 1.4.24.

    See also

    `make_transient_to_detached()` - provides for an alternative means of “merging” a single object into the `Session`

  attribute `sqlalchemy.orm.Session.` new

    The set of all instances marked as ‘new’ within this `Session`.

  attribute `sqlalchemy.orm.Session.` no_autoflush

    Return a context manager that disables autoflush.

    e.g.:

        with session.no_autoflush:

            some_object = SomeClass()
            session.add(some_object)
            # won't autoflush
            some_object.related_thing = session.query(SomeRelated).first()

    Operations that proceed within the `with:` block will not be subject to flushes occurring upon query access. This is useful when initializing a series of objects which involve existing database queries, where the uncompleted object should not yet be flushed.

  classmethod `sqlalchemy.orm.Session.` object_session(instance: object) → Session | None

    inherited from the `sqlalchemy.orm.session._SessionClassMethods.object_session` method of `sqlalchemy.orm.session._SessionClassMethods`

    Return the `Session` to which an object belongs.

    This is an alias of `object_session()`.

  method `sqlalchemy.orm.Session.` prepare() → None

    Prepare the current transaction in progress for two phase commit.

    If no transaction is in progress, this method raises an `InvalidRequestError`.

    Only root transactions of two phase sessions can be prepared. If the current transaction is not such, an `InvalidRequestError` is raised.

  method `sqlalchemy.orm.Session.` query(*entities: _ColumnsClauseArgument[Any], **kwargs: Any) → Query [Any]

    Return a new `Query` object corresponding to this `Session`.

    Note that the `Query` object is legacy as of SQLAlchemy 2.0; the `select()` construct is now used to construct ORM queries.

    See also

    SQLAlchemy Unified Tutorial

    ORM Querying Guide

    Legacy Query API - legacy API doc

  method `sqlalchemy.orm.Session.` refresh(instance: object, attribute_names: Iterable[str] | None = None, with_for_update: ForUpdateParameter = None) → None

    Expire and refresh attributes on the given instance.

    The selected attributes will first be expired as they would when using `Session.expire()`; then a SELECT statement will be issued to the database to refresh column-oriented attributes with the current value available in the current transaction.

    `relationship()` oriented attributes will also be immediately loaded if they were already eagerly loaded on the object, using the same eager loading strategy that they were loaded with originally.

    New in version 1.4: - the `Session.refresh()` method can also refresh eagerly loaded attributes.

    `relationship()` oriented attributes that would normally load using the `select` (or “lazy”) loader strategy will also load if they are named explicitly in the attribute_names collection, emitting a SELECT statement for the attribute using the `immediate` loader strategy. If lazy-loaded relationships are not named in `Session.refresh.attribute_names`, then they remain as “lazy loaded” attributes and are not implicitly refreshed.

    Changed in version 2.0.4: The `Session.refresh()` method will now refresh lazy-loaded `relationship()` oriented attributes for those which are named explicitly in the `Session.refresh.attribute_names` collection.

    Tip

    While the `Session.refresh()` method is capable of refreshing both column and relationship oriented attributes, its primary focus is on refreshing of local column-oriented attributes on a single instance. For more open ended “refresh” functionality, including the ability to refresh the attributes on many objects at once while having explicit control over relationship loader strategies, use the populate existing feature instead.

    Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction. Refreshing attributes usually only makes sense at the start of a transaction where database rows have not yet been accessed.

    Parameters:

      - attribute_names – optional. An iterable collection of string attribute names indicating a subset of attributes to be refreshed.

      - with_for_update – optional boolean `True` indicating FOR UPDATE should be used, or may be a dictionary containing flags to indicate a more specific set of FOR UPDATE flags for the SELECT; flags should match the parameters of `Query.with_for_update()`. Supersedes the `Session.refresh.lockmode` parameter.

    See also

    Refreshing / Expiring - introductory material

    `Session.expire()`

    `Session.expire_all()`

    Populate Existing - allows any ORM query to refresh objects as they would be loaded normally.

  method `sqlalchemy.orm.Session.` reset() → None

    Close out the transactional resources and ORM objects used by this `Session`, resetting the session to its initial state.

    This method provides for same “reset-only” behavior that the `Session.close()` method has provided historically, where the state of the `Session` is reset as though the object were brand new, and ready to be used again. This method may then be useful for `Session` objects which set `Session.close_resets_only` to `False`, so that “reset only” behavior is still available.

    New in version 2.0.22.

    See also

    Closing - detail on the semantics of `Session.close()` and `Session.reset()`.

    `Session.close()` - a similar method will additionally prevent re-use of the Session when the parameter `Session.close_resets_only` is set to `False`.

  method `sqlalchemy.orm.Session.` rollback() → None

    Rollback the current transaction in progress.

    If no transaction is in progress, this method is a pass-through.

    The method always rolls back the topmost database transaction, discarding any nested transactions that may be in progress.

    See also

    Rolling Back

    Managing Transactions

  method `sqlalchemy.orm.Session.` scalar(statement: Executable, params: _CoreSingleExecuteParams | None = None, *, execution_options: OrmExecuteOptionsParameter = {}, bind_arguments: _BindArguments | None = None, **kw: Any) → Any

    Execute a statement and return a scalar result.

    Usage and parameters are the same as that of `Session.execute()`; the return result is a scalar Python value.

  method `sqlalchemy.orm.Session.` scalars(statement: Executable, params: _CoreAnyExecuteParams | None = None, *, execution_options: OrmExecuteOptionsParameter = {}, bind_arguments: _BindArguments | None = None, **kw: Any) → ScalarResult [Any]

    Execute a statement and return the results as scalars.

    Usage and parameters are the same as that of `Session.execute()`; the return result is a `ScalarResult` filtering object which will return single elements rather than `Row` objects.

    Returns:

      a `ScalarResult` object

    New in version 1.4.24: Added `Session.scalars()`

    New in version 1.4.26: Added `scoped_session.scalars()`

    See also

    Selecting ORM Entities - contrasts the behavior of `Session.execute()` to `Session.scalars()`

class sqlalchemy.orm.SessionTransaction

  A `Session`-level transaction.

  `SessionTransaction` is produced from the `Session.begin()` and `Session.begin_nested()` methods. It’s largely an internal object that in modern use provides a context manager for session transactions.

  Documentation on interacting with `SessionTransaction` is at: Managing Transactions.

  Changed in version 1.4: The scoping and API methods to work with the `SessionTransaction` object directly have been simplified.

  See also

  Managing Transactions

  `Session.begin()`

  `Session.begin_nested()`

  `Session.rollback()`

  `Session.commit()`

  `Session.in_transaction()`

  `Session.in_nested_transaction()`

  `Session.get_transaction()`

  `Session.get_nested_transaction()`

  Members

  nested, origin, parent

  Class signature

  class `sqlalchemy.orm.SessionTransaction` (`sqlalchemy.orm.state_changes._StateChange`, `sqlalchemy.engine.util.TransactionalContext`)

  attribute `sqlalchemy.orm.SessionTransaction.` nested: bool = False

    Indicates if this is a nested, or SAVEPOINT, transaction.

    When `SessionTransaction.nested` is True, it is expected that `SessionTransaction.parent` will be present as well, linking to the enclosing `SessionTransaction`.

    See also

    `SessionTransaction.origin`

  attribute `sqlalchemy.orm.SessionTransaction.` origin: SessionTransactionOrigin

    Origin of this `SessionTransaction`.

    Refers to a `SessionTransactionOrigin` instance which is an enumeration indicating the source event that led to constructing this `SessionTransaction`.

    New in version 2.0.

  attribute `sqlalchemy.orm.SessionTransaction.` parent

    The parent `SessionTransaction` of this `SessionTransaction`.

    If this attribute is `None`, indicates this `SessionTransaction` is at the top of the stack, and corresponds to a real “COMMIT”/”ROLLBACK” block. If non-`None`, then this is either a “subtransaction” (an internal marker object used by the flush process) or a “nested” / SAVEPOINT transaction. If the `SessionTransaction.nested` attribute is `True`, then this is a SAVEPOINT, and if `False`, indicates this a subtransaction.

class sqlalchemy.orm.SessionTransactionOrigin

  indicates the origin of a `SessionTransaction`.

  This enumeration is present on the `SessionTransaction.origin` attribute of any `SessionTransaction` object.

  New in version 2.0.

  Members

  AUTOBEGIN, BEGIN, BEGIN_NESTED, SUBTRANSACTION

  Class signature

  class `sqlalchemy.orm.SessionTransactionOrigin` (`enum.Enum`)

  attribute `sqlalchemy.orm.SessionTransactionOrigin.` AUTOBEGIN = 0

    transaction were started by autobegin

  attribute `sqlalchemy.orm.SessionTransactionOrigin.` BEGIN = 1

    transaction were started by calling `Session.begin()`

  attribute `sqlalchemy.orm.SessionTransactionOrigin.` BEGIN_NESTED = 2

    tranaction were started by `Session.begin_nested()`

  attribute `sqlalchemy.orm.SessionTransactionOrigin.` SUBTRANSACTION = 3

    transaction is an internal “subtransaction”

## Session Utilities

Object Name | Description
--- | ---
close_all_sessions() | Close all sessions in memory.
make_transient(instance) | Alter the state of the given instance so that it is transient.
make_transient_to_detached(instance) | Make the given transient instance detached.
object_session(instance) | Return the `Session` to which the given instance belongs.
was_deleted(object_) | Return True if the given object was deleted within a session flush.

function sqlalchemy.orm.close_all_sessions() → None

  Close all sessions in memory.

  This function consults a global registry of all `Session` objects and calls `Session.close()` on them, which resets them to a clean state.

  This function is not for general use but may be useful for test suites within the teardown scheme.

  New in version 1.3.

function sqlalchemy.orm.make_transient(instance: object) → None

  Alter the state of the given instance so that it is transient.

  Note

  `make_transient()` is a special-case function for advanced use cases only.

  The given mapped instance is assumed to be in the persistent or detached state. The function will remove its association with any `Session` as well as its `InstanceState.identity`. The effect is that the object will behave as though it were newly constructed, except retaining any attribute / collection values that were loaded at the time of the call. The `InstanceState.deleted` flag is also reset if this object had been deleted as a result of using `Session.delete()`.

  Warning

  `make_transient()` does not “unexpire” or otherwise eagerly load ORM-mapped attributes that are not currently loaded at the time the function is called. This includes attributes which:

  - were expired via `Session.expire()`

  - were expired as the natural effect of committing a session transaction, e.g. `Session.commit()`

  - are normally lazy loaded but are not currently loaded

  - are “deferred” (see Limiting which Columns Load with Column Deferral) and are not yet loaded

  - were not present in the query which loaded this object, such as that which is common in joined table inheritance and other scenarios.

  After `make_transient()` is called, unloaded attributes such as those above will normally resolve to the value `None` when accessed, or an empty collection for a collection-oriented attribute. As the object is transient and un-associated with any database identity, it will no longer retrieve these values.

  See also

  `make_transient_to_detached()`

function sqlalchemy.orm.make_transient_to_detached(instance: object) → None

  Make the given transient instance detached.

  Note

  `make_transient_to_detached()` is a special-case function for advanced use cases only.

  All attribute history on the given instance will be reset as though the instance were freshly loaded from a query. Missing attributes will be marked as expired. The primary key attributes of the object, which are required, will be made into the “key” of the instance.

  The object can then be added to a session, or merged possibly with the load=False flag, at which point it will look as if it were loaded that way, without emitting SQL.

  This is a special use case function that differs from a normal call to `Session.merge()` in that a given persistent state can be manufactured without any SQL calls.

  See also

  `make_transient()`

  `Session.enable_relationship_loading()`

function sqlalchemy.orm.object_session(instance: object) → Session | None

  Return the `Session` to which the given instance belongs.

  This is essentially the same as the `InstanceState.session` accessor. See that attribute for details.

function sqlalchemy.orm.util.was_deleted(object_: object) → bool

  Return True if the given object was deleted within a session flush.

  This is regardless of whether or not the object is persistent or detached.

  See also

  `InstanceState.was_deleted`

## Attribute and State Management Utilities

These functions are provided by the SQLAlchemy attribute instrumentation API to provide a detailed interface for dealing with instances, attribute values, and history. Some of them are useful when constructing event listener functions, such as those described in ORM Events.

Object Name | Description
--- | ---
del_attribute(instance, key) | Delete the value of an attribute, firing history events.
flag_dirty(instance) | Mark an instance as ‘dirty’ without any specific attribute mentioned.
flag_modified(instance, key) | Mark an attribute on an instance as ‘modified’.
get_attribute(instance, key) | Get the value of an attribute, firing any callables required.
get_history(obj, key[, passive]) | Return a `History` record for the given object and attribute key.
History | A 3-tuple of added, unchanged and deleted values, representing the changes which have occurred on an instrumented attribute.
init_collection(obj, key) | Initialize a collection attribute and return the collection adapter.
instance_state | Return the `InstanceState` for a given mapped object.
is_instrumented(instance, key) | Return True if the given attribute on the given instance is instrumented by the attributes package.
object_state(instance) | Given an object, return the `InstanceState` associated with the object.
set_attribute(instance, key, value[, initiator]) | Set the value of an attribute, firing history events.
set_committed_value(instance, key, value) | Set the value of an attribute with no history events.

function sqlalchemy.orm.util.object_state(instance: _T) → InstanceState [_T]

  Given an object, return the `InstanceState` associated with the object.

  Raises `sqlalchemy.orm.exc.UnmappedInstanceError` if no mapping is configured.

  Equivalent functionality is available via the `inspect()` function as:

      inspect(instance)

  Using the inspection system will raise `sqlalchemy.exc.NoInspectionAvailable` if the instance is not part of a mapping.

function sqlalchemy.orm.attributes.del_attribute(instance: object, key: str) → None

  Delete the value of an attribute, firing history events.

  This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to establish attribute state as understood by SQLAlchemy.

function sqlalchemy.orm.attributes.get_attribute(instance: object, key: str) → Any

  Get the value of an attribute, firing any callables required.

  This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to make usage of attribute state as understood by SQLAlchemy.

function sqlalchemy.orm.attributes.get_history(obj: object, key: str, passive: PassiveFlag = symbol('PASSIVE_OFF')) → History

  Return a `History` record for the given object and attribute key.

  This is the pre-flush history for a given attribute, which is reset each time the `Session` flushes changes to the current database transaction.

  Note

  Prefer to use the `AttributeState.history` and `AttributeState.load_history()` accessors to retrieve the `History` for instance attributes.

  Parameters:

    - obj – an object whose class is instrumented by the attributes package.

    - key – string attribute name.

    - passive – indicates loading behavior for the attribute if the value is not already present. This is a bitflag attribute, which defaults to the symbol `PASSIVE_OFF` indicating all necessary SQL should be emitted.

  See also

  `AttributeState.history`

  `AttributeState.load_history()` - retrieve history using loader callables if the value is not locally present.

function sqlalchemy.orm.attributes.init_collection(obj: object, key: str) → CollectionAdapter

  Initialize a collection attribute and return the collection adapter.

  This function is used to provide direct access to collection internals for a previously unloaded attribute. e.g.:

      collection_adapter = init_collection(someobject, 'elements')
      for elem in values:
          collection_adapter.append_without_event(elem)

  For an easier way to do the above, see `set_committed_value()`.

  Parameters:

    - obj – a mapped object

    - key – string attribute name where the collection is located.

function sqlalchemy.orm.attributes.flag_modified(instance: object, key: str) → None

  Mark an attribute on an instance as ‘modified’.

  This sets the ‘modified’ flag on the instance and establishes an unconditional change event for the given attribute. The attribute must have a value present, else an `InvalidRequestError` is raised.

  To mark an object “dirty” without referring to any specific attribute so that it is considered within a flush, use the `flag_dirty()` call.

  See also

  `flag_dirty()`

function sqlalchemy.orm.attributes.flag_dirty(instance: object) → None

  Mark an instance as ‘dirty’ without any specific attribute mentioned.

  This is a special operation that will allow the object to travel through the flush process for interception by events such as `SessionEvents.before_flush()`. Note that no SQL will be emitted in the flush process for an object that has no changes, even if marked dirty via this method. However, a `SessionEvents.before_flush()` handler will be able to see the object in the `Session.dirty` collection and may establish changes on it, which will then be included in the SQL emitted.

  New in version 1.2.

  See also

  `flag_modified()`

function sqlalchemy.orm.attributes.instance_state()

  Return the `InstanceState` for a given mapped object.

  This function is the internal version of `object_state()`. The `object_state()` and/or the `inspect()` function is preferred here as they each emit an informative exception if the given object is not mapped.

function sqlalchemy.orm.instrumentation.is_instrumented(instance, key)

  Return True if the given attribute on the given instance is instrumented by the attributes package.

  This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required.

function sqlalchemy.orm.attributes.set_attribute(instance: object, key: str, value: Any, initiator: AttributeEventToken | None = None) → None

  Set the value of an attribute, firing history events.

  This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to establish attribute state as understood by SQLAlchemy.

  Parameters:

    - instance – the object that will be modified

    - key – string name of the attribute

    - value – value to assign

    - initiator –

      an instance of `Event` that would have been propagated from a previous event listener. This argument is used when the `set_attribute()` function is being used within an existing event listening function where an `Event` object is being supplied; the object may be used to track the origin of the chain of events.

      New in version 1.2.3.

function sqlalchemy.orm.attributes.set_committed_value(instance, key, value)

  Set the value of an attribute with no history events.

  Cancels any previous history present. The value should be a scalar value for scalar-holding attributes, or an iterable for any collection-holding attribute.

  This is the same underlying method used when a lazy loader fires off and loads additional data from the database. In particular, this method can be used by application code which has loaded additional attributes or collections through separate queries, which can then be attached to an instance as though it were part of its original loaded state.

class sqlalchemy.orm.attributes.History

  A 3-tuple of added, unchanged and deleted values, representing the changes which have occurred on an instrumented attribute.

  The easiest way to get a `History` object for a particular attribute on an object is to use the `inspect()` function:

      from sqlalchemy import inspect

      hist = inspect(myobject).attrs.myattribute.history

  Each tuple member is an iterable sequence:

  - `added` - the collection of items added to the attribute (the first tuple element).

  - `unchanged` - the collection of items that have not changed on the attribute (the second tuple element).

  - `deleted` - the collection of items that have been removed from the attribute (the third tuple element).

  Members

  added, deleted, empty(), has_changes(), non_added(), non_deleted(), sum(), unchanged

  Class signature

  class `sqlalchemy.orm.History` (`builtins.tuple`)

  attribute `sqlalchemy.orm.attributes.History.` added: Tuple[()] | List[Any]

    Alias for field number 0

  attribute `sqlalchemy.orm.attributes.History.` deleted: Tuple[()] | List[Any]

    Alias for field number 2

  method `sqlalchemy.orm.attributes.History.` empty() → bool

    Return True if this `History` has no changes and no existing, unchanged state.

  method `sqlalchemy.orm.attributes.History.` has_changes() → bool

    Return True if this `History` has changes.

  method `sqlalchemy.orm.attributes.History.` non_added() → Sequence[Any]

    Return a collection of unchanged + deleted.

  method `sqlalchemy.orm.attributes.History.` non_deleted() → Sequence[Any]

    Return a collection of added + unchanged.

  method `sqlalchemy.orm.attributes.History.` sum() → Sequence[Any]

    Return a collection of added + unchanged + deleted.

  attribute `sqlalchemy.orm.attributes.History.` unchanged: Tuple[()] | List[Any]

    Alias for field number 1