From 3b85eeb5d2e662141139ad54ccaad5df24ad9b7d Mon Sep 17 00:00:00 2001
From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Tue, 10 Sep 2019 12:46:21 -0400
Subject: [PATCH] Restore subquery.as_scalar() w/ deprecation

Apparently Alias had an .as_scalar() method, so restore an
equivalent to Subquery with an appropriate deprecation warning.

Fixes: #4854
Change-Id: I6255d61b7d82487ca90ba8ee79d4b3a74e7cbe38
---
 doc/build/changelog/unreleased_14/4617_scalar.rst |  5 ++++-
 lib/sqlalchemy/sql/selectable.py                  | 12 ++++++++++++
 test/sql/test_deprecations.py                     |  9 +++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/doc/build/changelog/unreleased_14/4617_scalar.rst b/doc/build/changelog/unreleased_14/4617_scalar.rst
index d47b3e464a..6fb4adcca7 100644
--- a/doc/build/changelog/unreleased_14/4617_scalar.rst
+++ b/doc/build/changelog/unreleased_14/4617_scalar.rst
@@ -13,7 +13,10 @@
     This warning will in a later major release become an error, however the
     message will always be clear when :meth:`.SelectBase.scalar_subquery` needs
     to be invoked.   The latter part of the change is for clarity and to reduce
-    the implicit decisionmaking by the query coercion system.
+    the implicit decisionmaking by the query coercion system.   The
+    :meth:`.Subquery.as_scalar` method, which was previously
+    ``Alias.as_scalar``, is also deprecated; ``.scalar_subquery()`` should be
+    invoked directly from ` :func:`.select` object or :class:`.Query` object.
 
     This change is part of the larger change to convert :func:`.select` objects
     to no longer be directly part of the "from clause" class hierarchy, which
diff --git a/lib/sqlalchemy/sql/selectable.py b/lib/sqlalchemy/sql/selectable.py
index 00d3826b21..166e592b62 100644
--- a/lib/sqlalchemy/sql/selectable.py
+++ b/lib/sqlalchemy/sql/selectable.py
@@ -1753,6 +1753,18 @@ class Subquery(AliasedReturnsRows):
             roles.SelectStatementRole, selectable
         ).subquery(name=name)
 
+    @util.deprecated(
+        "1.4",
+        "The :meth:`.Subquery.as_scalar` method, which was previously "
+        "``Alias.as_scalar()`` prior to version 1.4, is deprecated and "
+        "will be removed in a future release; Please use the "
+        ":meth:`.Select.scalar_subquery` method of the :func:`.select` "
+        "construct before constructing a subquery object, or with the ORM "
+        "use the :meth:`.Query.scalar_subquery` method.",
+    )
+    def as_scalar(self):
+        return self.element.scalar_subquery()
+
 
 class FromGrouping(GroupedElement, FromClause):
     """Represent a grouping of a FROM clause"""
diff --git a/test/sql/test_deprecations.py b/test/sql/test_deprecations.py
index d126912a5d..09deb12944 100644
--- a/test/sql/test_deprecations.py
+++ b/test/sql/test_deprecations.py
@@ -579,6 +579,15 @@ class SubqueryCoercionsTest(fixtures.TestBase, AssertsCompiledSQL):
 
         is_true(stmt.compare(select([self.table1.c.myid]).scalar_subquery()))
 
+    def test_as_scalar_from_subquery(self):
+        with testing.expect_deprecated(
+            r"The Subquery.as_scalar\(\) method, which was previously "
+            r"``Alias.as_scalar\(\)`` prior to version 1.4"
+        ):
+            stmt = select([self.table1.c.myid]).subquery().as_scalar()
+
+        is_true(stmt.compare(select([self.table1.c.myid]).scalar_subquery()))
+
     def test_fromclause_subquery(self):
         stmt = select([self.table1.c.myid])
         with testing.expect_deprecated(
-- 
2.47.2