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Edit File: engine.py
# future/engine.py # Copyright (C) 2005-2024 the SQLAlchemy authors and contributors # <see AUTHORS file> # # This module is part of SQLAlchemy and is released under # the MIT License: https://www.opensource.org/licenses/mit-license.php from .. import util from ..engine import Connection as _LegacyConnection from ..engine import create_engine as _create_engine from ..engine import Engine as _LegacyEngine from ..engine.base import OptionEngineMixin NO_OPTIONS = util.immutabledict() def create_engine(*arg, **kw): """Create a new :class:`_future.Engine` instance. Arguments passed to :func:`_future.create_engine` are mostly identical to those passed to the 1.x :func:`_sa.create_engine` function. The difference is that the object returned is the :class:`._future.Engine` which has the 2.0 version of the API. """ kw["_future_engine_class"] = Engine return _create_engine(*arg, **kw) class Connection(_LegacyConnection): """Provides high-level functionality for a wrapped DB-API connection. The :class:`_future.Connection` object is procured by calling the :meth:`_future.Engine.connect` method of the :class:`_future.Engine` object, and provides services for execution of SQL statements as well as transaction control. **This is the SQLAlchemy 2.0 version** of the :class:`_engine.Connection` class. The API and behavior of this object is largely the same, with the following differences in behavior: * The result object returned for results is the :class:`_engine.CursorResult` object, which is a subclass of the :class:`_engine.Result`. This object has a slightly different API and behavior than the :class:`_engine.LegacyCursorResult` returned for 1.x style usage. * The object has :meth:`_future.Connection.commit` and :meth:`_future.Connection.rollback` methods which commit or roll back the current transaction in progress, if any. * The object features "autobegin" behavior, such that any call to :meth:`_future.Connection.execute` will unconditionally start a transaction which can be controlled using the above mentioned :meth:`_future.Connection.commit` and :meth:`_future.Connection.rollback` methods. * The object does not have any "autocommit" functionality. Any SQL statement or DDL statement will not be followed by any COMMIT until the transaction is explicitly committed, either via the :meth:`_future.Connection.commit` method, or if the connection is being used in a context manager that commits such as the one returned by :meth:`_future.Engine.begin`. * The SAVEPOINT method :meth:`_future.Connection.begin_nested` returns a :class:`_engine.NestedTransaction` as was always the case, and the savepoint can be controlled by invoking :meth:`_engine.NestedTransaction.commit` or :meth:`_engine.NestedTransaction.rollback` as was the case before. However, this savepoint "transaction" is not associated with the transaction that is controlled by the connection itself; the overall transaction can be committed or rolled back directly which will not emit any special instructions for the SAVEPOINT (this will typically have the effect that one desires). * The :class:`_future.Connection` object does not support "branching", which was a pattern by which a sub "connection" would be used that refers to this connection as a parent. """ _is_future = True def _branch(self): raise NotImplementedError( "sqlalchemy.future.Connection does not support " "'branching' of new connections." ) def begin(self): """Begin a transaction prior to autobegin occurring. The returned object is an instance of :class:`_engine.RootTransaction`. This object represents the "scope" of the transaction, which completes when either the :meth:`_engine.Transaction.rollback` or :meth:`_engine.Transaction.commit` method is called. The :meth:`_future.Connection.begin` method in SQLAlchemy 2.0 begins a transaction that normally will be begun in any case when the connection is first used to execute a statement. The reason this method might be used would be to invoke the :meth:`_events.ConnectionEvents.begin` event at a specific time, or to organize code within the scope of a connection checkout in terms of context managed blocks, such as:: with engine.connect() as conn: with conn.begin(): conn.execute(...) conn.execute(...) with conn.begin(): conn.execute(...) conn.execute(...) The above code is not fundamentally any different in its behavior than the following code which does not use :meth:`_future.Connection.begin`; the below style is referred towards as "commit as you go" style:: with engine.connect() as conn: conn.execute(...) conn.execute(...) conn.commit() conn.execute(...) conn.execute(...) conn.commit() From a database point of view, the :meth:`_future.Connection.begin` method does not emit any SQL or change the state of the underlying DBAPI connection in any way; the Python DBAPI does not have any concept of explicit transaction begin. .. seealso:: :ref:`tutorial_working_with_transactions` - in the :ref:`unified_tutorial` :meth:`_future.Connection.begin_nested` - use a SAVEPOINT :meth:`_engine.Connection.begin_twophase` - use a two phase /XID transaction :meth:`_future.Engine.begin` - context manager available from :class:`_future.Engine` """ return super(Connection, self).begin() def begin_nested(self): """Begin a nested transaction (i.e. SAVEPOINT) and return a transaction handle. The returned object is an instance of :class:`_engine.NestedTransaction`. Nested transactions require SAVEPOINT support in the underlying database. Any transaction in the hierarchy may ``commit`` and ``rollback``, however the outermost transaction still controls the overall ``commit`` or ``rollback`` of the transaction of a whole. If an outer :class:`.RootTransaction` is not present on this :class:`_future.Connection`, a new one is created using "autobegin". This outer transaction may be completed using "commit-as-you-go" style usage, by calling upon :meth:`_future.Connection.commit` or :meth:`_future.Connection.rollback`. .. tip:: The "autobegin" behavior of :meth:`_future.Connection.begin_nested` is specific to :term:`2.0 style` use; for legacy behaviors, see :meth:`_engine.Connection.begin_nested`. The :class:`_engine.NestedTransaction` remains independent of the :class:`_future.Connection` object itself. Calling the :meth:`_future.Connection.commit` or :meth:`_future.Connection.rollback` will always affect the actual containing database transaction itself, and not the SAVEPOINT itself. When a database transaction is committed, any SAVEPOINTs that have been established are cleared and the data changes within their scope is also committed. .. seealso:: :meth:`_future.Connection.begin` """ return super(Connection, self).begin_nested() def commit(self): """Commit the transaction that is currently in progress. This method commits the current transaction if one has been started. If no transaction was started, the method has no effect, assuming the connection is in a non-invalidated state. A transaction is begun on a :class:`_future.Connection` automatically whenever a statement is first executed, or when the :meth:`_future.Connection.begin` method is called. .. note:: The :meth:`_future.Connection.commit` method only acts upon the primary database transaction that is linked to the :class:`_future.Connection` object. It does not operate upon a SAVEPOINT that would have been invoked from the :meth:`_future.Connection.begin_nested` method; for control of a SAVEPOINT, call :meth:`_engine.NestedTransaction.commit` on the :class:`_engine.NestedTransaction` that is returned by the :meth:`_future.Connection.begin_nested` method itself. """ if self._transaction: self._transaction.commit() def rollback(self): """Roll back the transaction that is currently in progress. This method rolls back the current transaction if one has been started. If no transaction was started, the method has no effect. If a transaction was started and the connection is in an invalidated state, the transaction is cleared using this method. A transaction is begun on a :class:`_future.Connection` automatically whenever a statement is first executed, or when the :meth:`_future.Connection.begin` method is called. .. note:: The :meth:`_future.Connection.rollback` method only acts upon the primary database transaction that is linked to the :class:`_future.Connection` object. It does not operate upon a SAVEPOINT that would have been invoked from the :meth:`_future.Connection.begin_nested` method; for control of a SAVEPOINT, call :meth:`_engine.NestedTransaction.rollback` on the :class:`_engine.NestedTransaction` that is returned by the :meth:`_future.Connection.begin_nested` method itself. """ if self._transaction: self._transaction.rollback() def close(self): """Close this :class:`_future.Connection`. This has the effect of also calling :meth:`_future.Connection.rollback` if any transaction is in place. """ super(Connection, self).close() def execute(self, statement, parameters=None, execution_options=None): r"""Executes a SQL statement construct and returns a :class:`_engine.Result`. :param statement: The statement to be executed. This is always an object that is in both the :class:`_expression.ClauseElement` and :class:`_expression.Executable` hierarchies, including: * :class:`_expression.Select` * :class:`_expression.Insert`, :class:`_expression.Update`, :class:`_expression.Delete` * :class:`_expression.TextClause` and :class:`_expression.TextualSelect` * :class:`_schema.DDL` and objects which inherit from :class:`_schema.DDLElement` :param parameters: parameters which will be bound into the statement. This may be either a dictionary of parameter names to values, or a mutable sequence (e.g. a list) of dictionaries. When a list of dictionaries is passed, the underlying statement execution will make use of the DBAPI ``cursor.executemany()`` method. When a single dictionary is passed, the DBAPI ``cursor.execute()`` method will be used. :param 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 :meth:`_future.Connection.execution_options`. :return: a :class:`_engine.Result` object. """ return self._execute_20( statement, parameters, execution_options or NO_OPTIONS ) def scalar(self, statement, parameters=None, execution_options=None): r"""Executes a SQL statement construct and returns a scalar object. This method is shorthand for invoking the :meth:`_engine.Result.scalar` method after invoking the :meth:`_future.Connection.execute` method. Parameters are equivalent. :return: a scalar Python value representing the first column of the first row returned. """ return self.execute(statement, parameters, execution_options).scalar() class Engine(_LegacyEngine): """Connects a :class:`_pool.Pool` and :class:`_engine.Dialect` together to provide a source of database connectivity and behavior. **This is the SQLAlchemy 2.0 version** of the :class:`~.engine.Engine`. An :class:`.future.Engine` object is instantiated publicly using the :func:`~sqlalchemy.future.create_engine` function. .. seealso:: :doc:`/core/engines` :ref:`connections_toplevel` """ _connection_cls = Connection _is_future = True def _not_implemented(self, *arg, **kw): raise NotImplementedError( "This method is not implemented for SQLAlchemy 2.0." ) transaction = ( run_callable ) = ( execute ) = ( scalar ) = ( _execute_clauseelement ) = _execute_compiled = table_names = has_table = _not_implemented def _run_ddl_visitor(self, visitorcallable, element, **kwargs): # TODO: this is for create_all support etc. not clear if we # want to provide this in 2.0, that is, a way to execute SQL where # they aren't calling "engine.begin()" explicitly, however, DDL # may be a special case for which we want to continue doing it this # way. A big win here is that the full DDL sequence is inside of a # single transaction rather than COMMIT for each statement. with self.begin() as conn: conn._run_ddl_visitor(visitorcallable, element, **kwargs) @classmethod def _future_facade(self, legacy_engine): return Engine( legacy_engine.pool, legacy_engine.dialect, legacy_engine.url, logging_name=legacy_engine.logging_name, echo=legacy_engine.echo, hide_parameters=legacy_engine.hide_parameters, execution_options=legacy_engine._execution_options, ) @util.contextmanager def begin(self): """Return a :class:`_future.Connection` object with a transaction begun. Use of this method is similar to that of :meth:`_future.Engine.connect`, typically as a context manager, which will automatically maintain the state of the transaction when the block ends, either by calling :meth:`_future.Connection.commit` when the block succeeds normally, or :meth:`_future.Connection.rollback` when an exception is raised, before propagating the exception outwards:: with engine.begin() as connection: connection.execute(text("insert into table values ('foo')")) .. seealso:: :meth:`_future.Engine.connect` :meth:`_future.Connection.begin` """ with self.connect() as conn: with conn.begin(): yield conn def connect(self): """Return a new :class:`_future.Connection` object. The :class:`_future.Connection` acts as a Python context manager, so the typical use of this method looks like:: with engine.connect() as connection: connection.execute(text("insert into table values ('foo')")) connection.commit() Where above, after the block is completed, the connection is "closed" and its underlying DBAPI resources are returned to the connection pool. This also has the effect of rolling back any transaction that was explicitly begun or was begun via autobegin, and will emit the :meth:`_events.ConnectionEvents.rollback` event if one was started and is still in progress. .. seealso:: :meth:`_future.Engine.begin` """ return super(Engine, self).connect() class OptionEngine(OptionEngineMixin, Engine): pass Engine._option_cls = OptionEngine