Add scalars method to connection and session classes

Added new methods :meth:`_orm.Session.scalars`,
:meth:`_engine.Connection.scalars`, :meth:`_asyncio.AsyncSession.scalars`
and :meth:`_asyncio.AsyncSession.stream_scalars`, which provide a short cut
to the use case of receiving a row-oriented :class:`_result.Result` object
and converting it to a :class:`_result.ScalarResult` object via the
:meth:`_engine.Result.scalars` method, to return a list of values rather
than a list of rows. The new methods are analogous to the long existing
:meth:`_orm.Session.scalar` and :meth:`_engine.Connection.scalar` methods
used to return a single value from the first row only. Pull request
courtesy Miguel Grinberg.

Fixes: #6990
Closes: #6991
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/6991
Pull-request-sha: b3e0bb3042c55b0cc5af6a25cb3f31b929f88a47

Change-Id: Ia445775e24ca964b0162c2c8e5ca67dd1e39199f

1 files changed, 41 insertions, 0 deletions

diff --git a/lib/sqlalchemy/ext/asyncio/engine.py b/lib/sqlalchemy/ext/asyncio/engine.py
index 5a692ffb1..ab29438ed 100644
--- a/lib/sqlalchemy/ext/asyncio/engine.py
+++ b/lib/sqlalchemy/ext/asyncio/engine.py
@@ -439,6 +439,47 @@ class AsyncConnection(ProxyComparable, StartableContext, AsyncConnectable):
         result = await self.execute(statement, parameters, execution_options)
         return result.scalar()
 
+    async def scalars(
+        self,
+        statement,
+        parameters=None,
+        execution_options=util.EMPTY_DICT,
+    ):
+        r"""Executes a SQL statement construct and returns a scalar objects.
+
+        This method is shorthand for invoking the
+        :meth:`_engine.Result.scalars` method after invoking the
+        :meth:`_future.Connection.execute` method.  Parameters are equivalent.
+
+        :return: a :class:`_engine.ScalarResult` object.
+
+        .. versionadded:: 1.4.24
+
+        """
+        result = await self.execute(statement, parameters, execution_options)
+        return result.scalars()
+
+    async def stream_scalars(
+        self,
+        statement,
+        parameters=None,
+        execution_options=util.EMPTY_DICT,
+    ):
+        r"""Executes a SQL statement and returns a streaming scalar result
+        object.
+
+        This method is shorthand for invoking the
+        :meth:`_engine.AsyncResult.scalars` method after invoking the
+        :meth:`_future.Connection.stream` method.  Parameters are equivalent.
+
+        :return: an :class:`_asyncio.AsyncScalarResult` object.
+
+        .. versionadded:: 1.4.24
+
+        """
+        result = await self.stream(statement, parameters, execution_options)
+        return result.scalars()
+
     async def run_sync(self, fn, *arg, **kw):
         """Invoke the given sync callable passing self as the first argument.