- Added new argument ``include_backrefs=True`` to the

:func:`.validates` function; when set to False, a validation event
will not be triggered if the event was initated as a backref to
an attribute operation from the other side. [ticket:1535]
- break out validation tests into an updated module test_validators

3 files changed, 45 insertions, 12 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 375e7b1af..9b91d0638 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -1103,11 +1103,10 @@ class Mapper(_InspectionAttr):
                     self._reconstructor = method
                     event.listen(manager, 'load', _event_on_load, raw=True)
                 elif hasattr(method, '__sa_validators__'):
-                    include_removes = getattr(method,
-                                            "__sa_include_removes__", False)
+                    validation_opts = method.__sa_validation_opts__
                     for name in method.__sa_validators__:
                         self.validators = self.validators.union(
-                            {name: (method, include_removes)}
+                            {name: (method, validation_opts)}
                         )
 
         manager.info[_INSTRUMENTOR] = self
@@ -2582,13 +2581,28 @@ def validates(*names, **kw):
      argument "is_remove" which will be a boolean.
 
      .. versionadded:: 0.7.7
+    :param include_backrefs: defaults to ``True``; if ``False``, the
+     validation function will not emit if the originator is an attribute
+     event related via a backref.  This can be used for bi-directional
+     :func:`.validates` usage where only one validator should emit per
+     attribute operation.
+
+     .. versionadded:: 0.9.0b2
+
+    .. seealso::
+
+      :ref:`simple_validators` - usage examples for :func:`.validates`
 
     """
     include_removes = kw.pop('include_removes', False)
+    include_backrefs = kw.pop('include_backrefs', True)
 
     def wrap(fn):
         fn.__sa_validators__ = names
-        fn.__sa_include_removes__ = include_removes
+        fn.__sa_validation_opts__ = {
+                  "include_removes": include_removes,
+                  "include_backrefs": include_backrefs
+                }
         return fn
     return wrap
 
diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index b04338d9c..8226a0e0f 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -44,10 +44,10 @@ def _register_attribute(strategy, mapper, useobject,
         listen_hooks.append(single_parent_validator)
 
     if prop.key in prop.parent.validators:
-        fn, include_removes = prop.parent.validators[prop.key]
+        fn, opts = prop.parent.validators[prop.key]
         listen_hooks.append(
             lambda desc, prop: orm_util._validator_events(desc,
-                                prop.key, fn, include_removes)
+                                prop.key, fn, **opts)
             )
 
     if useobject:
diff --git a/lib/sqlalchemy/orm/util.py b/lib/sqlalchemy/orm/util.py
index 1b8f53c9d..b86672175 100644
--- a/lib/sqlalchemy/orm/util.py
+++ b/lib/sqlalchemy/orm/util.py
@@ -70,24 +70,43 @@ class CascadeOptions(frozenset):
         )
 
 
-def _validator_events(desc, key, validator, include_removes):
+def _validator_events(desc, key, validator, include_removes, include_backrefs):
     """Runs a validation method on an attribute value to be set or appended."""
 
+    if not include_backrefs:
+        def detect_is_backref(state, initiator):
+            impl = state.manager[key].impl
+            return initiator.impl is not impl
+
     if include_removes:
         def append(state, value, initiator):
-            return validator(state.obj(), key, value, False)
+            if include_backrefs or not detect_is_backref(state, initiator):
+                return validator(state.obj(), key, value, False)
+            else:
+                return value
 
         def set_(state, value, oldvalue, initiator):
-            return validator(state.obj(), key, value, False)
+            if include_backrefs or not detect_is_backref(state, initiator):
+                return validator(state.obj(), key, value, False)
+            else:
+                return value
 
         def remove(state, value, initiator):
-            validator(state.obj(), key, value, True)
+            if include_backrefs or not detect_is_backref(state, initiator):
+                validator(state.obj(), key, value, True)
+
     else:
         def append(state, value, initiator):
-            return validator(state.obj(), key, value)
+            if include_backrefs or not detect_is_backref(state, initiator):
+                return validator(state.obj(), key, value)
+            else:
+                return value
 
         def set_(state, value, oldvalue, initiator):
-            return validator(state.obj(), key, value)
+            if include_backrefs or not detect_is_backref(state, initiator):
+                return validator(state.obj(), key, value)
+            else:
+                return value
 
     event.listen(desc, 'append', append, raw=True, retval=True)
     event.listen(desc, 'set', set_, raw=True, retval=True)