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