Warnings for @declared_attr.cascadingticket_4091

A warning is emitted if a subclass attempts to override an attribute
that was declared on a superclass using ``@declared_attr.cascading``
that the overridden attribute will be ignored. This use
case cannot be fully supported down to further subclasses without more
complex development efforts, so for consistency the "cascading" is
honored all the way down regardless of overriding attributes.

A warning is emitted if the ``@declared_attr.cascading`` attribute is
used with a special declarative name such as ``__tablename__``, as this
has no effect.

Ensure that documenation refers to the current inconsistency that
__tablename__ can be overridden by subclasses however
@declared_attr.cascading cannot.

Fixes: #4091
Fixes: #4092
Change-Id: I3aecdb2f99d408e404a1223f5ad86ae3c7fdf036

1 files changed, 40 insertions, 1 deletions

diff --git a/test/ext/declarative/test_mixin.py b/test/ext/declarative/test_mixin.py
index be169bcda..0b1b117fb 100644
--- a/test/ext/declarative/test_mixin.py
+++ b/test/ext/declarative/test_mixin.py
@@ -1,5 +1,5 @@
 from sqlalchemy.testing import eq_, assert_raises, \
-    assert_raises_message, is_
+    assert_raises_message, is_, expect_warnings
 from sqlalchemy.ext import declarative as decl
 import sqlalchemy as sa
 from sqlalchemy import testing
@@ -1613,6 +1613,30 @@ class DeclaredAttrTest(DeclarativeTestBase, testing.AssertsCompiledSQL):
 
         eq_(counter.mock_calls, [mock.call(A), mock.call(B)])
 
+    def test_property_cascade_mixin_override(self):
+        counter = mock.Mock()
+
+        class Mixin(object):
+            @declared_attr.cascading
+            def my_prop(cls):
+                counter(cls)
+                return column_property(cls.x + 2)
+
+        class A(Base, Mixin):
+            __tablename__ = 'a'
+
+            id = Column(Integer, primary_key=True)
+            x = Column(Integer)
+
+        with expect_warnings(
+                "Attribute 'my_prop' on class .*B.* "
+                "cannot be processed due to @declared_attr.cascading; "
+                "skipping"):
+            class B(A):
+                my_prop = Column('foobar', Integer)
+
+        eq_(counter.mock_calls, [mock.call(A), mock.call(B)])
+
     def test_property_cascade_abstract(self):
         counter = mock.Mock()
 
@@ -1635,6 +1659,21 @@ class DeclaredAttrTest(DeclarativeTestBase, testing.AssertsCompiledSQL):
 
         eq_(counter.mock_calls, [mock.call(A), mock.call(B)])
 
+    def test_warn_cascading_used_w_tablename(self):
+        class Mixin(object):
+            @declared_attr.cascading
+            def __tablename__(cls):
+                return "foo"
+
+        with expect_warnings(
+            "@declared_attr.cascading is not supported on the "
+            "__tablename__ attribute on class .*A."
+        ):
+            class A(Mixin, Base):
+                id = Column(Integer, primary_key=True)
+
+        eq_(A.__table__.name, "foo")
+
     def test_col_prop_attrs_associated_w_class_for_mapper_args(self):
         from sqlalchemy import Column
         import collections