- Custom comparator classes used in conjunction with

column_property(), relation() etc. can define
new comparison methods on the Comparator, which will
become available via __getattr__() on the
InstrumentedAttribute.   In the case of synonym()
or comparable_property(), attributes are resolved first
on the user-defined descriptor, then on the user-defined
comparator.

2 files changed, 26 insertions, 3 deletions

diff --git a/lib/sqlalchemy/orm/attributes.py b/lib/sqlalchemy/orm/attributes.py
index df607adf8..2b2760208 100644
--- a/lib/sqlalchemy/orm/attributes.py
+++ b/lib/sqlalchemy/orm/attributes.py
@@ -131,7 +131,17 @@ class QueryableAttribute(interfaces.PropComparator):
 
     def hasparent(self, state, optimistic=False):
         return self.impl.hasparent(state, optimistic=optimistic)
-
+    
+    def __getattr__(self, key):
+        try:
+            return getattr(self.comparator, key)
+        except AttributeError:
+            raise AttributeError('Neither %r object nor %r object has an attribute %r' % (
+                    type(self).__name__, 
+                    type(self.comparator).__name__, 
+                    key)
+            )
+        
     def __str__(self):
         return repr(self.parententity) + "." + self.property.key
 
@@ -195,8 +205,19 @@ def proxied_attribute_factory(descriptor):
             return descriptor.__delete__(instance)
 
         def __getattr__(self, attribute):
-            """Delegate __getattr__ to the original descriptor."""
-            return getattr(descriptor, attribute)
+            """Delegate __getattr__ to the original descriptor and/or comparator."""
+            
+            try:
+                return getattr(descriptor, attribute)
+            except AttributeError:
+                try:
+                    return getattr(self._comparator, attribute)
+                except AttributeError:
+                    raise AttributeError('Neither %r object nor %r object has an attribute %r' % (
+                            type(descriptor).__name__, 
+                            type(self._comparator).__name__, 
+                            attribute)
+                    )
 
         def _property(self):
             return self._parententity.get_property(self.key, resolve_synonyms=True)
diff --git a/lib/sqlalchemy/orm/properties.py b/lib/sqlalchemy/orm/properties.py
index bf9bda366..675b505e7 100644
--- a/lib/sqlalchemy/orm/properties.py
+++ b/lib/sqlalchemy/orm/properties.py
@@ -42,6 +42,7 @@ class ColumnProperty(StrategizedProperty):
         self.group = kwargs.pop('group', None)
         self.deferred = kwargs.pop('deferred', False)
         self.comparator_factory = kwargs.pop('comparator_factory', self.__class__.Comparator)
+        self.descriptor = kwargs.pop('descriptor', None)
         self.extension = kwargs.pop('extension', None)
         util.set_creation_order(self)
         if self.deferred:
@@ -206,6 +207,7 @@ class SynonymProperty(MapperProperty):
                     if obj is None:
                         return s
                     return getattr(obj, self.name)
+
             self.descriptor = SynonymProp()
 
         def comparator_callable(prop, mapper):