Track SchemaEventTarget types in as_mutable()

Fixed bug in :mod:`sqlalchemy.ext.mutable` where the
:meth:`.Mutable.as_mutable` method would not track a type that had
been copied using :meth:`.TypeEngine.copy`.  This became more of
a regression in 1.1 compared to 1.0 because the :class:`.TypeDecorator`
class is now a subclass of :class:`.SchemaEventTarget`, which among
other things indicates to the parent :class:`.Column` that the type
should be copied when the :class:`.Column` is.  These copies are
common when using declarative with mixins or abstract classes.

Change-Id: Ib04df862c58263185dbae686c548fea3e12c46f1
Fixes: #3950

1 files changed, 43 insertions, 0 deletions

diff --git a/test/ext/test_mutable.py b/test/ext/test_mutable.py
index 81d2136e3..5b6d3e7cf 100644
--- a/test/ext/test_mutable.py
+++ b/test/ext/test_mutable.py
@@ -725,6 +725,49 @@ class MutableWithScalarJSONTest(_MutableDictTestBase, fixtures.MappedTest):
         self._test_non_mutable()
 
 
+class MutableColumnCopyJSONTest(_MutableDictTestBase, fixtures.MappedTest):
+
+    @classmethod
+    def define_tables(cls, metadata):
+        import json
+        from sqlalchemy.ext.declarative import declarative_base
+
+        class JSONEncodedDict(TypeDecorator):
+            impl = VARCHAR(50)
+
+            def process_bind_param(self, value, dialect):
+                if value is not None:
+                    value = json.dumps(value)
+
+                return value
+
+            def process_result_value(self, value, dialect):
+                if value is not None:
+                    value = json.loads(value)
+                return value
+
+        MutableDict = cls._type_fixture()
+
+        Base = declarative_base(metadata=metadata)
+
+        class AbstractFoo(Base):
+            __abstract__ = True
+
+            id = Column(Integer, primary_key=True,
+                        test_needs_autoincrement=True)
+            data = Column(MutableDict.as_mutable(JSONEncodedDict))
+            non_mutable_data = Column(JSONEncodedDict)
+            unrelated_data = Column(String(50))
+
+        class Foo(AbstractFoo):
+            __tablename__ = "foo"
+
+        assert Foo.data.property.columns[0].type is not AbstractFoo.data.type
+
+    def test_non_mutable(self):
+        self._test_non_mutable()
+
+
 class MutableListWithScalarPickleTest(_MutableListTestBase,
                                       fixtures.MappedTest):