Return given type when it matches the adaptation

The rules for type coercion between :class:`.Numeric`, :class:`.Integer`,
and date-related types now include additional logic that will attempt
to preserve the settings of the incoming type on the "resolved" type.
Currently the target for this is the ``asdecimal`` flag, so that
a math operation between :class:`.Numeric` or :class:`.Float` and
:class:`.Integer` will preserve the "asdecimal" flag as well as
if the type should be the :class:`.Float` subclass.

Change-Id: Idfaba17220d6db21ca1ca4dcb4c19834cd397817
Fixes: #4018

1 files changed, 24 insertions, 2 deletions

diff --git a/test/sql/test_types.py b/test/sql/test_types.py
index 9107adaca..404d42c7a 100644
--- a/test/sql/test_types.py
+++ b/test/sql/test_types.py
@@ -29,6 +29,8 @@ from sqlalchemy.testing.util import picklers
 from sqlalchemy.testing.util import round_decimal
 from sqlalchemy.testing import fixtures
 from sqlalchemy.testing import mock
+from sqlalchemy.sql import column
+import operator
 
 
 class AdaptTest(fixtures.TestBase):
@@ -2203,8 +2205,6 @@ class ExpressionTest(
         eq_(expr.type._type_affinity, types.Interval)
 
     def test_numerics_coercion(self):
-        from sqlalchemy.sql import column
-        import operator
 
         for op in (operator.add, operator.mul, operator.truediv, operator.sub):
             for other in (Numeric(10, 2), Integer):
@@ -2219,6 +2219,28 @@ class ExpressionTest(
                 )
                 assert isinstance(expr.type, types.Numeric)
 
+    def test_asdecimal_int_to_numeric(self):
+        expr = column('a', Integer) * column('b', Numeric(asdecimal=False))
+        is_(expr.type.asdecimal, False)
+
+        expr = column('a', Integer) * column('b', Numeric())
+        is_(expr.type.asdecimal, True)
+
+        expr = column('a', Integer) * column('b', Float())
+        is_(expr.type.asdecimal, False)
+        assert isinstance(expr.type, Float)
+
+    def test_asdecimal_numeric_to_int(self):
+        expr = column('a', Numeric(asdecimal=False)) * column('b', Integer)
+        is_(expr.type.asdecimal, False)
+
+        expr = column('a', Numeric()) * column('b', Integer)
+        is_(expr.type.asdecimal, True)
+
+        expr = column('a', Float()) * column('b', Integer)
+        is_(expr.type.asdecimal, False)
+        assert isinstance(expr.type, Float)
+
     def test_null_comparison(self):
         eq_(
             str(column('a', types.NullType()) + column('b', types.NullType())),