Release: 2.0.31 | Release Date: June 18, 2024

# SQLAlchemy 2.0 Documentation

# Contextual/Thread-local Sessions

Recall from the section When do I construct a Session, when do I commit it, and when do I close it?, the concept of “session scopes” was introduced, with an emphasis on web applications and the practice of linking the scope of a `Session` with that of a web request. Most modern web frameworks include integration tools so that the scope of the `Session` can be managed automatically, and these tools should be used as they are available.

SQLAlchemy includes its own helper object, which helps with the establishment of user-defined `Session` scopes. It is also used by third-party integration systems to help construct their integration schemes.

The object is the `scoped_session` object, and it represents a registry of `Session` objects. If you’re not familiar with the registry pattern, a good introduction can be found in Patterns of Enterprise Architecture.

Warning

The `scoped_session` registry by default uses a Python `threading.local()` in order to track `Session` instances. This is not necessarily compatible with all application servers, particularly those which make use of greenlets or other alternative forms of concurrency control, which may lead to race conditions (e.g. randomly occurring failures) when used in moderate to high concurrency scenarios. Please read Thread-Local Scope and Using Thread-Local Scope with Web Applications below to more fully understand the implications of using `threading.local()` to track `Session` objects and consider more explicit means of scoping when using application servers which are not based on traditional threads.

Note

The `scoped_session` object is a very popular and useful object used by many SQLAlchemy applications. However, it is important to note that it presents only one approach to the issue of `Session` management. If you’re new to SQLAlchemy, and especially if the term “thread-local variable” seems strange to you, we recommend that if possible you familiarize first with an off-the-shelf integration system such as Flask-SQLAlchemy or zope.sqlalchemy.

A `scoped_session` is constructed by calling it, passing it a factory which can create new `Session` objects. A factory is just something that produces a new object when called, and in the case of `Session`, the most common factory is the `sessionmaker`, introduced earlier in this section. Below we illustrate this usage:

    >>> from sqlalchemy.orm import scoped_session
    >>> from sqlalchemy.orm import sessionmaker

    >>> session_factory = sessionmaker(bind=some_engine)
    >>> Session = scoped_session(session_factory)

The `scoped_session` object we’ve created will now call upon the `sessionmaker` when we “call” the registry:

    >>> some_session = Session()

Above, `some_session` is an instance of `Session`, which we can now use to talk to the database. This same `Session` is also present within the `scoped_session` registry we’ve created. If we call upon the registry a second time, we get back the same `Session`:

    >>> some_other_session = Session()
    >>> some_session is some_other_session
    True

This pattern allows disparate sections of the application to call upon a global `scoped_session`, so that all those areas may share the same session without the need to pass it explicitly. The `Session` we’ve established in our registry will remain, until we explicitly tell our registry to dispose of it, by calling `scoped_session.remove()`:

    >>> Session.remove()

The `scoped_session.remove()` method first calls `Session.close()` on the current `Session`, which has the effect of releasing any connection/transactional resources owned by the `Session` first, then discarding the `Session` itself. “Releasing” here means that connections are returned to their connection pool and any transactional state is rolled back, ultimately using the `rollback()` method of the underlying DBAPI connection.

At this point, the `scoped_session` object is “empty”, and will create a new `Session` when called again. As illustrated below, this is not the same `Session` we had before:

    >>> new_session = Session()
    >>> new_session is some_session
    False

The above series of steps illustrates the idea of the “registry” pattern in a nutshell. With that basic idea in hand, we can discuss some of the details of how this pattern proceeds.

## Implicit Method Access

The job of the `scoped_session` is simple; hold onto a `Session` for all who ask for it. As a means of producing more transparent access to this `Session`, the `scoped_session` also includes proxy behavior, meaning that the registry itself can be treated just like a `Session` directly; when methods are called on this object, they are proxied to the underlying `Session` being maintained by the registry:

    Session = scoped_session(some_factory)

    # equivalent to:
    #
    # session = Session()
    # print(session.scalars(select(MyClass)).all())
    #
    print(Session.scalars(select(MyClass)).all())

The above code accomplishes the same task as that of acquiring the current `Session` by calling upon the registry, then using that `Session`.

## Thread-Local Scope

Users who are familiar with multithreaded programming will note that representing anything as a global variable is usually a bad idea, as it implies that the global object will be accessed by many threads concurrently. The `Session` object is entirely designed to be used in a non-concurrent fashion, which in terms of multithreading means “only in one thread at a time”. So our above example of `scoped_session` usage, where the same `Session` object is maintained across multiple calls, suggests that some process needs to be in place such that multiple calls across many threads don’t actually get a handle to the same session. We call this notion thread local storage, which means, a special object is used that will maintain a distinct object per each application thread. Python provides this via the threading.local() construct. The `scoped_session` object by default uses this object as storage, so that a single `Session` is maintained for all who call upon the `scoped_session` registry, but only within the scope of a single thread. Callers who call upon the registry in a different thread get a `Session` instance that is local to that other thread.

Using this technique, the `scoped_session` provides a quick and relatively simple (if one is familiar with thread-local storage) way of providing a single, global object in an application that is safe to be called upon from multiple threads.

The `scoped_session.remove()` method, as always, removes the current `Session` associated with the thread, if any. However, one advantage of the `threading.local()` object is that if the application thread itself ends, the “storage” for that thread is also garbage collected. So it is in fact “safe” to use thread local scope with an application that spawns and tears down threads, without the need to call `scoped_session.remove()`. However, the scope of transactions themselves, i.e. ending them via `Session.commit()` or `Session.rollback()`, will usually still be something that must be explicitly arranged for at the appropriate time, unless the application actually ties the lifespan of a thread to the lifespan of a transaction.

## Using Thread-Local Scope with Web Applications

As discussed in the section When do I construct a Session, when do I commit it, and when do I close it?, a web application is architected around the concept of a web request, and integrating such an application with the `Session` usually implies that the `Session` will be associated with that request. As it turns out, most Python web frameworks, with notable exceptions such as the asynchronous frameworks Twisted and Tornado, use threads in a simple way, such that a particular web request is received, processed, and completed within the scope of a single worker thread. When the request ends, the worker thread is released to a pool of workers where it is available to handle another request.

This simple correspondence of web request and thread means that to associate a `Session` with a thread implies it is also associated with the web request running within that thread, and vice versa, provided that the `Session` is created only after the web request begins and torn down just before the web request ends. So it is a common practice to use `scoped_session` as a quick way to integrate the `Session` with a web application. The sequence diagram below illustrates this flow:

    Web Server          Web Framework        SQLAlchemy ORM Code
    --------------      --------------       ------------------------------
    startup        ->   Web framework        # Session registry is established
                        initializes          Session = scoped_session(sessionmaker())

    incoming
    web request    ->   web request     ->   # The registry is *optionally*
                        starts               # called upon explicitly to create
                                             # a Session local to the thread and/or request
                                             Session()

                                             # the Session registry can otherwise
                                             # be used at any time, creating the
                                             # request-local Session() if not present,
                                             # or returning the existing one
                                             Session.execute(select(MyClass)) # ...

                                             Session.add(some_object) # ...

                                             # if data was modified, commit the
                                             # transaction
                                             Session.commit()

                        web request ends  -> # the registry is instructed to
                                             # remove the Session
                                             Session.remove()

                        sends output      <-
    outgoing web    <-
    response

Using the above flow, the process of integrating the `Session` with the web application has exactly two requirements:

1. Create a single `scoped_session` registry when the web application first starts, ensuring that this object is accessible by the rest of the application.

2. Ensure that `scoped_session.remove()` is called when the web request ends, usually by integrating with the web framework’s event system to establish an “on request end” event.

As noted earlier, the above pattern is just one potential way to integrate a `Session` with a web framework, one which in particular makes the significant assumption that the web framework associates web requests with application threads. It is however strongly recommended that the integration tools provided with the web framework itself be used, if available, instead of `scoped_session`.

In particular, while using a thread local can be convenient, it is preferable that the `Session` be associated directly with the request, rather than with the current thread. The next section on custom scopes details a more advanced configuration which can combine the usage of `scoped_session` with direct request based scope, or any kind of scope.

## Using Custom Created Scopes

The `scoped_session` object’s default behavior of “thread local” scope is only one of many options on how to “scope” a `Session`. A custom scope can be defined based on any existing system of getting at “the current thing we are working with”.

Suppose a web framework defines a library function `get_current_request()`. An application built using this framework can call this function at any time, and the result will be some kind of `Request` object that represents the current request being processed. If the `Request` object is hashable, then this function can be easily integrated with `scoped_session` to associate the `Session` with the request. Below we illustrate this in conjunction with a hypothetical event marker provided by the web framework `on_request_end`, which allows code to be invoked whenever a request ends:

    from my_web_framework import get_current_request, on_request_end
    from sqlalchemy.orm import scoped_session, sessionmaker

    Session = scoped_session(sessionmaker(bind=some_engine), scopefunc=get_current_request)

    @on_request_end
    def remove_session(req):
        Session.remove()

Above, we instantiate `scoped_session` in the usual way, except that we pass our request-returning function as the “scopefunc”. This instructs `scoped_session` to use this function to generate a dictionary key whenever the registry is called upon to return the current `Session`. In this case it is particularly important that we ensure a reliable “remove” system is implemented, as this dictionary is not otherwise self-managed.

## Contextual Session API

Object Name | Description
--- | ---
QueryPropertyDescriptor | Describes the type applied to a class-level `scoped_session.query_property()` attribute.
scoped_session | Provides scoped management of `Session` objects.
ScopedRegistry | A Registry that can store one or multiple instances of a single class on the basis of a “scope” function.
ThreadLocalRegistry | A `ScopedRegistry` that uses a `threading.local()` variable for storage.

class sqlalchemy.orm.scoped_session

  Provides scoped management of `Session` objects.

  See Contextual/Thread-local Sessions for a tutorial.

  Note

  When using Asynchronous I/O (asyncio), the async-compatible `async_scoped_session` class should be used in place of `scoped_session`.

  Members

  __call__(), __init__(), add(), add_all(), autoflush, begin(), begin_nested(), bind, bulk_insert_mappings(), bulk_save_objects(), bulk_update_mappings(), close(), close_all(), commit(), configure(), connection(), delete(), deleted, dirty, execute(), expire(), expire_all(), expunge(), expunge_all(), flush(), get(), get_bind(), get_one(), identity_key(), identity_map, info, is_active, is_modified(), merge(), new, no_autoflush, object_session(), query(), query_property(), refresh(), remove(), reset(), rollback(), scalar(), scalars(), session_factory

  Class signature

  class `sqlalchemy.orm.scoped_session` (`typing.Generic`)

  method `sqlalchemy.orm.scoped_session.`__call__(**kw: Any) → _S

    Return the current `Session`, creating it using the `scoped_session.session_factory` if not present.

    Parameters:

      **kw – Keyword arguments will be passed to the `scoped_session.session_factory` callable, if an existing `Session` is not present. If the `Session` is present and keyword arguments have been passed, `InvalidRequestError` is raised.

  method `sqlalchemy.orm.scoped_session.`__init__(session_factory: sessionmaker[_S], scopefunc: Callable[[], Any] | None = None)

    Construct a new `scoped_session`.

    Parameters:

      - session_factory – a factory to create new `Session` instances. This is usually, but not necessarily, an instance of `sessionmaker`.

      - scopefunc – optional function which defines the current scope. If not passed, the `scoped_session` object assumes “thread-local” scope, and will use a Python `threading.local()` in order to maintain the current `Session`. If passed, the function should return a hashable token; this token will be used as the key in a dictionary in order to store and retrieve the current `Session`.

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

    Place an object into this `Session`.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`add_all(instances: Iterable[object]) → None

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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

  attribute `sqlalchemy.orm.scoped_session.`autoflush

    Proxy for the `Session.autoflush` attribute on behalf of the `scoped_session` class.

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

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`begin_nested() → SessionTransaction

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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).

  attribute `sqlalchemy.orm.scoped_session.`bind

    Proxy for the `Session.bind` attribute on behalf of the `scoped_session` class.

  method `sqlalchemy.orm.scoped_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.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_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.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`bulk_update_mappings(mapper: Mapper[Any], mappings: Iterable[Dict[str, Any]]) → None

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`close() → None

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`close_all() → None

    Close all sessions in memory.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`commit() → None

    Flush pending changes and commit the current transaction.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`configure(**kwargs: Any) → None

    reconfigure the `sessionmaker` used by this `scoped_session`.

    See `sessionmaker.configure()`.

  method `sqlalchemy.orm.scoped_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.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`delete(instance: object) → None

    Mark an instance as deleted.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`deleted

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

  attribute `sqlalchemy.orm.scoped_session.`dirty

    The set of all persistent instances considered dirty.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_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.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`expire(instance: object, attribute_names: Iterable[str] | None = None) → None

    Expire the attributes on an instance.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`expire_all() → None

    Expires all persistent instances within this Session.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`expunge(instance: object) → None

    Remove the instance from this `Session`.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

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

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

    Remove all object instances from this `Session`.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

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

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

    Flush all the object changes to the database.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_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.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_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.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_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.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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

  classmethod `sqlalchemy.orm.scoped_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]

    Return an identity key.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    This is an alias of `identity_key()`.

  attribute `sqlalchemy.orm.scoped_session.`identity_map

    Proxy for the `Session.identity_map` attribute on behalf of the `scoped_session` class.

  attribute `sqlalchemy.orm.scoped_session.`info

    A user-modifiable dictionary.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.

  attribute `sqlalchemy.orm.scoped_session.`is_active

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`is_modified(instance: object, include_collections: bool = True) → bool

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    This method retrieves the history for each instrumented attribute on the instance and performs a comparison of the current value to its previously flushed or 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.scoped_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`.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    `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.scoped_session.`new

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

  attribute `sqlalchemy.orm.scoped_session.`no_autoflush

    Return a context manager that disables autoflush.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`object_session(instance: object) → Session | None

    Return the `Session` to which an object belongs.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    This is an alias of `object_session()`.

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

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`query_property(query_cls: Type[Query[_T]] | None = None) → QueryPropertyDescriptor

    return a class property which produces a legacy `Query` object against the class and the current `Session` when called.

    Legacy Feature

    The `scoped_session.query_property()` accessor is specific to the legacy `Query` object and is not considered to be part of 2.0-style ORM use.

    e.g.:

        from sqlalchemy.orm import QueryPropertyDescriptor
        from sqlalchemy.orm import scoped_session
        from sqlalchemy.orm import sessionmaker

        Session = scoped_session(sessionmaker())

        class MyClass:
            query: QueryPropertyDescriptor = Session.query_property()

        # after mappers are defined
        result = MyClass.query.filter(MyClass.name=='foo').all()

    Produces instances of the session’s configured query class by default. To override and use a custom implementation, provide a `query_cls` callable. The callable will be invoked with the class’s mapper as a positional argument and a session keyword argument.

    There is no limit to the number of query properties placed on a class.

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

    Expire and refresh attributes on the given instance.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`remove() → None

    Dispose of the current `Session`, if present.

    This will first call `Session.close()` method on the current `Session`, which releases any existing transactional/connection resources still being held; transactions specifically are rolled back. The `Session` is then discarded. Upon next usage within the same scope, the `scoped_session` will produce a new `Session` object.

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

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

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_session.`rollback() → None

    Rollback the current transaction in progress.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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.scoped_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.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

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

  method `sqlalchemy.orm.scoped_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.

    Proxied for the `Session` class on behalf of the `scoped_session` class.

    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()`

  attribute `sqlalchemy.orm.scoped_session.`session_factory: sessionmaker[_S]

    The session_factory provided to __init__ is stored in this attribute and may be accessed at a later time. This can be useful when a new non-scoped `Session` is needed.

class sqlalchemy.util.ScopedRegistry

  A Registry that can store one or multiple instances of a single class on the basis of a “scope” function.

  The object implements `__call__` as the “getter”, so by calling `myregistry()` the contained object is returned for the current scope.

  Parameters:

    - createfunc – a callable that returns a new object to be placed in the registry

    - scopefunc – a callable that will return a key to store/retrieve an object.

  Members

  __init__(), clear(), has(), set()

  Class signature

  class `sqlalchemy.util.ScopedRegistry` (`typing.Generic`)

  method `sqlalchemy.util.ScopedRegistry.`__init__(createfunc: Callable[[], _T], scopefunc: Callable[[], Any])

    Construct a new `ScopedRegistry`.

    Parameters:

      - createfunc – A creation function that will generate a new value for the current scope, if none is present.

      - scopefunc – A function that returns a hashable token representing the current scope (such as, current thread identifier).

  method `sqlalchemy.util.ScopedRegistry.`clear() → None

    Clear the current scope, if any.

  method `sqlalchemy.util.ScopedRegistry.`has() → bool

    Return True if an object is present in the current scope.

  method `sqlalchemy.util.ScopedRegistry.`set(obj: _T) → None

    Set the value for the current scope.

class sqlalchemy.util.ThreadLocalRegistry

  A `ScopedRegistry` that uses a `threading.local()` variable for storage.

  Class signature

  class `sqlalchemy.util.ThreadLocalRegistry` (`sqlalchemy.util.ScopedRegistry`)

class sqlalchemy.orm.QueryPropertyDescriptor

  Describes the type applied to a class-level `scoped_session.query_property()` attribute.

  New in version 2.0.5.

  Class signature

  class `sqlalchemy.orm.QueryPropertyDescriptor` (`typing_extensions.Protocol`)