- Fixed a regression regarding the :meth:`.MapperEvents.instrument_class`

event where its invocation was moved to be after the class manager's
instrumentation of the class, which is the opposite of what the
documentation for the event explicitly states.  The rationale for the
switch was due to Declarative taking the step of setting up
the full "instrumentation manager" for a class before it was mapped
for the purpose of the new ``@declared_attr`` features
described in :ref:`feature_3150`, but the change was also made
against the classical use of :func:`.mapper` for consistency.
However, SQLSoup relies upon the instrumentation event happening
before any instrumentation under classical mapping.
The behavior is reverted in the case of classical and declarative
mapping, the latter implemented by using a simple memoization
without using class manager.
fixes #3388

1 files changed, 8 insertions, 13 deletions

diff --git a/lib/sqlalchemy/ext/declarative/api.py b/lib/sqlalchemy/ext/declarative/api.py
index 713ea0aba..3d46bd4cb 100644
--- a/lib/sqlalchemy/ext/declarative/api.py
+++ b/lib/sqlalchemy/ext/declarative/api.py
@@ -163,21 +163,16 @@ class declared_attr(interfaces._MappedAttribute, property):
         self._cascading = cascading
 
     def __get__(desc, self, cls):
-        # use the ClassManager for memoization of values.  This is better than
-        # adding yet another attribute onto the class, or using weakrefs
-        # here which are slow and take up memory.  It also allows us to
-        # warn for non-mapped use of declared_attr.
-
-        manager = attributes.manager_of_class(cls)
-        if manager is None:
-            util.warn(
-                "Unmanaged access of declarative attribute %s from "
-                "non-mapped class %s" %
-                (desc.fget.__name__, cls.__name__))
+        reg = cls.__dict__.get('_sa_declared_attr_reg', None)
+        if reg is None:
+            manager = attributes.manager_of_class(cls)
+            if manager is None:
+                util.warn(
+                    "Unmanaged access of declarative attribute %s from "
+                    "non-mapped class %s" %
+                    (desc.fget.__name__, cls.__name__))
             return desc.fget(cls)
 
-        reg = manager.info.get('declared_attr_reg', None)
-
         if reg is None:
             return desc.fget(cls)
         elif desc in reg: