- Loosened some restrictions that were added to ``@declared_attr``

objects, such that they were prevented from being called outside
of the declarative process; this is related to the enhancements
of #3150 which allow ``@declared_attr`` to return a value that is
cached based on the current class as it's being configured.
The exception raise has been removed, and the behavior changed
so that outside of the declarative process, the function decorated by
``@declared_attr`` is called every time just like a regular
``@property``, without using any caching, as none is available
at this stage.
fixes #3331

3 files changed, 54 insertions, 9 deletions

diff --git a/doc/build/changelog/changelog_10.rst b/doc/build/changelog/changelog_10.rst
index 6d8aa67da..70f31f5e6 100644
--- a/doc/build/changelog/changelog_10.rst
+++ b/doc/build/changelog/changelog_10.rst
@@ -19,6 +19,21 @@
     :version: 1.0.0b2
 
     .. change::
+        :tags: change, ext, declarative
+        :tickets: 3331
+
+        Loosened some restrictions that were added to ``@declared_attr``
+        objects, such that they were prevented from being called outside
+        of the declarative process; this is related to the enhancements
+        of #3150 which allow ``@declared_attr`` to return a value that is
+        cached based on the current class as it's being configured.
+        The exception raise has been removed, and the behavior changed
+        so that outside of the declarative process, the function decorated by
+        ``@declared_attr`` is called every time just like a regular
+        ``@property``, without using any caching, as none is available
+        at this stage.
+
+    .. change::
         :tags: bug, engine
         :tickets: 3330, 3329
 
diff --git a/lib/sqlalchemy/ext/declarative/api.py b/lib/sqlalchemy/ext/declarative/api.py
index 048533b92..713ea0aba 100644
--- a/lib/sqlalchemy/ext/declarative/api.py
+++ b/lib/sqlalchemy/ext/declarative/api.py
@@ -175,15 +175,12 @@ class declared_attr(interfaces._MappedAttribute, property):
                 "non-mapped class %s" %
                 (desc.fget.__name__, cls.__name__))
             return desc.fget(cls)
-        try:
-            reg = manager.info['declared_attr_reg']
-        except KeyError:
-            raise exc.InvalidRequestError(
-                "@declared_attr called outside of the "
-                "declarative mapping process; is declarative_base() being "
-                "used correctly?")
-
-        if desc in reg:
+
+        reg = manager.info.get('declared_attr_reg', None)
+
+        if reg is None:
+            return desc.fget(cls)
+        elif desc in reg:
             return reg[desc]
         else:
             reg[desc] = obj = desc.fget(cls)
diff --git a/test/ext/declarative/test_mixin.py b/test/ext/declarative/test_mixin.py
index 5cefe8d47..45b881671 100644
--- a/test/ext/declarative/test_mixin.py
+++ b/test/ext/declarative/test_mixin.py
@@ -1392,6 +1392,39 @@ class DeclaredAttrTest(DeclarativeTestBase, testing.AssertsCompiledSQL):
             getattr, Mixin, "my_prop"
         )
 
+    def test_non_decl_access(self):
+        counter = mock.Mock()
+
+        class Mixin(object):
+            @declared_attr
+            def __tablename__(cls):
+                counter(cls)
+                return "foo"
+
+        class Foo(Mixin, Base):
+            id = Column(Integer, primary_key=True)
+
+            @declared_attr
+            def x(cls):
+                cls.__tablename__
+
+            @declared_attr
+            def y(cls):
+                cls.__tablename__
+
+        eq_(
+            counter.mock_calls,
+            [mock.call(Foo)]
+        )
+
+        eq_(Foo.__tablename__, 'foo')
+        eq_(Foo.__tablename__, 'foo')
+
+        eq_(
+            counter.mock_calls,
+            [mock.call(Foo), mock.call(Foo), mock.call(Foo)]
+        )
+
     def test_property_noncascade(self):
         counter = mock.Mock()