Session API

Session and sessionmaker()

Object NameDescription

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.:

  1. from sqlalchemy import create_engine
  2. from sqlalchemy.orm import sessionmaker
  4. # an Engine, which the Session will use for connection
  5. # resources
  6. engine = create_engine('postgresql+psycopg2://scott:tiger@localhost/')
  8. Session = sessionmaker(engine)
  10. with Session() as session:
  11.     session.add(some_object)
  12.     session.add(some_other_object)
  13.     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:

  1. session = Session()
  2. try:
  3.     session.add(some_object)
  4.     session.add(some_other_object)
  5.     session.commit()
  6. finally:
  7.     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:

  1. Session = sessionmaker(engine)
  3. with Session.begin() as session:
  4.     session.add(some_object)
  5.     session.add(some_other_object)
  6. # 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:

  1. Session = sessionmaker(engine)
  3. # bind an individual session to a connection
  5. with engine.connect() as connection:
  6.     with Session(bind=connection) as session:
  7.         # 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:

  1. # application starts, sessionmaker does not have
  2. # an engine bound yet
  3. Session = sessionmaker()
  5. # ... later, when an engine URL is read from a configuration
  6. # file or other events allow the engine to be created
  7. engine = create_engine('sqlite:///foo.db')
  8. Session.configure(bind=engine)
  10. sess = Session()
  11. # 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:

    1. Session = sessionmaker(some_engine)
    2. 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.:

    1. Session = sessionmaker(some_engine)
    3. with Session.begin() as session:
    4.     session.add(some_object)
    6. # 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.:

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

  • classmethod sqlalchemy.orm.sessionmaker.identity_key(class\: Optional[Type[Any]] = None, _ident: Union[Any, Tuple[Any, …]] = None, *, instance: Optional[Any] = None, row: Optional[Union[Row[Any], RowMapping]] = None, identity_token: Optional[Any] = 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) → Optional[Session]

    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)

class sqlalchemy.orm.Session

Manages persistence operations for ORM-mapped objects.

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_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(), rollback(), scalar(), scalars()

Class signature

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

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

    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:

        1. Session = sessionmaker(binds={
        2.     SomeMappedClass: create_engine('postgresql+psycopg2://engine1'),
        3.     SomeDeclarativeBase: create_engine('postgresql+psycopg2://engine2'),
        4.     some_mapper: create_engine('postgresql+psycopg2://engine3'),
        5.     some_table: create_engine('postgresql+psycopg2://engine4'),
        6.     })

        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 section Serializable isolation / Savepoints / Transactional DDL 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.

  1. See also
  3. [Partitioning Strategies (e.g. multiple database backends per Session)]($47efe01e33821e5c.md#session-partitioning)
  5. [Session.binds](#sqlalchemy.orm.Session.params.binds "sqlalchemy.orm.Session")
  7. [Session.bind\_table()](#sqlalchemy.orm.Session.bind_table "sqlalchemy.orm.Session.bind_table")
  1. See also
  3. [Partitioning Strategies (e.g. multiple database backends per Session)]($47efe01e33821e5c.md#session-partitioning)
  5. [Session.binds](#sqlalchemy.orm.Session.params.binds "sqlalchemy.orm.Session")
  7. [Session.bind\_mapper()](#sqlalchemy.orm.Session.bind_mapper "sqlalchemy.orm.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.

  1. See also
  3. [ORM-Enabled INSERT, UPDATE, and DELETE statements]($8137f13cfe1f7fec.md)
  5. [Session.bulk\_save\_objects()](#sqlalchemy.orm.Session.bulk_save_objects "sqlalchemy.orm.Session.bulk_save_objects")
  7. [Session.bulk\_update\_mappings()](#sqlalchemy.orm.Session.bulk_update_mappings "sqlalchemy.orm.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.

  1. See also
  3. [ORM-Enabled INSERT, UPDATE, and DELETE statements]($8137f13cfe1f7fec.md)
  5. [Session.bulk\_insert\_mappings()](#sqlalchemy.orm.Session.bulk_insert_mappings "sqlalchemy.orm.Session.bulk_insert_mappings")
  7. [Session.bulk\_update\_mappings()](#sqlalchemy.orm.Session.bulk_update_mappings "sqlalchemy.orm.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.

  1. See also
  3. [ORM-Enabled INSERT, UPDATE, and DELETE statements]($8137f13cfe1f7fec.md)
  5. [Session.bulk\_insert\_mappings()](#sqlalchemy.orm.Session.bulk_insert_mappings "sqlalchemy.orm.Session.bulk_insert_mappings")
  7. [Session.bulk\_save\_objects()](#sqlalchemy.orm.Session.bulk_save_objects "sqlalchemy.orm.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

    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.

    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()

  • 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: Optional[_BindArguments] = None, execution_options: Optional[_ExecuteOptions] = 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.

  • 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.:

    1. 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: Optional[_CoreAnyExecuteParams] = None, *, execution_options: OrmExecuteOptionsParameter = {}, bind_arguments: Optional[_BindArguments] = None, _parent_execute_state: Optional[Any] = None, _add_event: Optional[Any] = None) → Result[Any]

    Execute a SQL expression construct.

    Returns a Result object representing results of the statement execution.

    E.g.:

    1. from sqlalchemy import select
    2. result = session.execute(
    3.     select(User).where(User.id == 5)
    4. )

    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: Optional[Iterable[str]] = 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.

  1. See also
  3. [Refreshing / Expiring]($592600365cded3ff.md#session-expire) - introductory material
  5. [Session.expire()](#sqlalchemy.orm.Session.expire "sqlalchemy.orm.Session.expire")
  7. [Session.refresh()](#sqlalchemy.orm.Session.refresh "sqlalchemy.orm.Session.refresh")
  9. [Query.populate\_existing()]($3d0cc000ec6c7150.md#sqlalchemy.orm.Query.populate_existing "sqlalchemy.orm.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: Optional[Sequence[Any]] = 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: Optional[Sequence[ORMOption]] = None, populate_existing: bool = False, with_for_update: Optional[ForUpdateArg] = None, identity_token: Optional[Any] = None, execution_options: OrmExecuteOptionsParameter = {}, bind_arguments: Optional[_BindArguments] = None) → Optional[_O]

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

    E.g.:

    1. my_user = session.get(User, 5)
    3. some_object = session.get(VersionedFoo, (5, 10))
    5. some_object = session.get(
    6.     VersionedFoo,
    7.     {"id": 5, "version_id": 10}
    8. )

    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:

        1. 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:

        1. 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:

        1. 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: Optional[_EntityBindKey[_O]] = None, *, clause: Optional[ClauseElement] = None, bind: Optional[_SessionBind] = None, _sa_skip_events: Optional[bool] = None, _sa_skip_for_implicit_returning: bool = False, **kw: Any) → Union[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.

  1. See also
  3. [Partitioning Strategies (e.g. multiple database backends per Session)]($47efe01e33821e5c.md#session-partitioning)
  5. [Session.binds](#sqlalchemy.orm.Session.params.binds "sqlalchemy.orm.Session")
  7. [Session.bind\_mapper()](#sqlalchemy.orm.Session.bind_mapper "sqlalchemy.orm.Session.bind_mapper")
  9. [Session.bind\_table()](#sqlalchemy.orm.Session.bind_table "sqlalchemy.orm.Session.bind_table")

  • method sqlalchemy.orm.Session.get_nested_transaction() → Optional[SessionTransaction]

    Return the current nested transaction in progress, if any.

    New in version 1.4.

  • method sqlalchemy.orm.Session.get_transaction() → Optional[SessionTransaction]

    Return the current root transaction in progress, if any.

    New in version 1.4.

  • classmethod sqlalchemy.orm.Session.identity_key(class\: Optional[Type[Any]] = None, _ident: Union[Any, Tuple[Any, …]] = None, *, instance: Optional[Any] = None, row: Optional[Union[Row[Any], RowMapping]] = None, identity_token: Optional[Any] = 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:

    1. import gevent
    3. try:
    4.     sess = Session()
    5.     sess.add(User())
    6.     sess.commit()
    7. except gevent.Timeout:
    8.     sess.invalidate()
    9.     raise
    10. except:
    11.     sess.rollback()
    12.     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.:

    1. 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: Optional[Sequence[ORMOption]] = 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.

    Changed in version 1.1: - Session.merge() will now reconcile pending objects with overlapping primary keys in the same way as persistent. See Session.merge resolves pending conflicts the same as persistent for discussion.

    • 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.

  1. See also
  3. [make\_transient\_to\_detached()](#sqlalchemy.orm.make_transient_to_detached "sqlalchemy.orm.make_transient_to_detached") - provides for an alternative means of “merging” a single object into the [Session](#sqlalchemy.orm.Session "sqlalchemy.orm.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.:

    1. with session.no_autoflush:
    3.     some_object = SomeClass()
    4.     session.add(some_object)
    5.     # won't autoflush
    6.     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) → Optional[Session]

    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: Optional[Iterable[str]] = None, with_for_update: Optional[ForUpdateArg] = 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. Unloaded relationship attributes will remain unloaded, as will relationship attributes that were originally lazy loaded.

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

    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.

  1. See also
  3. [Refreshing / Expiring]($592600365cded3ff.md#session-expire) - introductory material
  5. [Session.expire()](#sqlalchemy.orm.Session.expire "sqlalchemy.orm.Session.expire")
  7. [Session.expire\_all()](#sqlalchemy.orm.Session.expire_all "sqlalchemy.orm.Session.expire_all")
  9. [Populate Existing]($661bd2ffd6937693.md#orm-queryguide-populate-existing) - allows any ORM query to refresh objects as they would be loaded normally.

  • 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: Optional[_CoreSingleExecuteParams] = None, *, execution_options: OrmExecuteOptionsParameter = {}, bind_arguments: Optional[_BindArguments] = 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: Optional[_CoreAnyExecuteParams] = None, *, execution_options: OrmExecuteOptionsParameter = {}, bind_arguments: Optional[_BindArguments] = 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.

    New in version 1.4.24.

    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)

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)

Session Utilities

Object NameDescription

closeall_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:

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) → Optional[Session]

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 NameDescription

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:

  1. 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.:

  1. collection_adapter = init_collection(someobject, 'elements')
  2. for elem in values:
  3.     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: Optional[AttributeEventToken] = 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:

  1. from sqlalchemy import inspect
  3. 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)