- Fixed bug that affected many classes of event, particularly

ORM events but also engine events, where the usual logic of
"de duplicating" a redundant call to :func:`.event.listen`
with the same arguments would fail, for those events where the
listener function is wrapped.  An assertion would be hit within
registry.py.  This assertion has now been integrated into the
deduplication check, with the added bonus of a simpler means
of checking deduplication across the board.
fixes #3199

doc/build/changelog/changelog_09.rst

@@ -13,6 +13,20 @@
 .. changelog::
     :version: 0.9.8
 
+    .. change::
+        :tags: bug, orm
+        :versions: 1.0.0
+        :tickets: 3199
+
+        Fixed bug that affected many classes of event, particularly
+        ORM events but also engine events, where the usual logic of
+        "de duplicating" a redundant call to :func:`.event.listen`
+        with the same arguments would fail, for those events where the
+        listener function is wrapped.  An assertion would be hit within
+        registry.py.  This assertion has now been integrated into the
+        deduplication check, with the added bonus of a simpler means
+        of checking deduplication across the board.
+
     .. change::
         :tags: bug, mssql
         :versions: 1.0.0

lib/sqlalchemy/event/attr.py

@@ -319,14 +319,12 @@ class _ListenerCollection(RefCollection, _CompoundListener):
         registry._stored_in_collection_multi(self, other, to_associate)
 
     def insert(self, event_key, propagate):
-        if event_key._listen_fn not in self.listeners:
-            event_key.prepend_to_list(self, self.listeners)
+        if event_key.prepend_to_list(self, self.listeners):
             if propagate:
                 self.propagate.add(event_key._listen_fn)
 
     def append(self, event_key, propagate):
-        if event_key._listen_fn not in self.listeners:
-            event_key.append_to_list(self, self.listeners)
+        if event_key.append_to_list(self, self.listeners):
             if propagate:
                 self.propagate.add(event_key._listen_fn)
 

lib/sqlalchemy/event/registry.py

@@ -71,13 +71,15 @@ def _stored_in_collection(event_key, owner):
     listen_ref = weakref.ref(event_key._listen_fn)
 
     if owner_ref in dispatch_reg:
-        assert dispatch_reg[owner_ref] == listen_ref
-    else:
-        dispatch_reg[owner_ref] = listen_ref
+        return False
+
+    dispatch_reg[owner_ref] = listen_ref
 
     listener_to_key = _collection_to_key[owner_ref]
     listener_to_key[listen_ref] = key
 
+    return True
+
 
 def _removed_from_collection(event_key, owner):
     key = event_key._key
@@ -229,18 +231,20 @@ class _EventKey(object):
     def _listen_fn(self):
         return self.fn_wrap or self.fn
 
-    def append_value_to_list(self, owner, list_, value):
-        _stored_in_collection(self, owner)
-        list_.append(value)
-
     def append_to_list(self, owner, list_):
-        _stored_in_collection(self, owner)
-        list_.append(self._listen_fn)
+        if _stored_in_collection(self, owner):
+            list_.append(self._listen_fn)
+            return True
+        else:
+            return False
 
     def remove_from_list(self, owner, list_):
         _removed_from_collection(self, owner)
         list_.remove(self._listen_fn)
 
     def prepend_to_list(self, owner, list_):
-        _stored_in_collection(self, owner)
-        list_.appendleft(self._listen_fn)
+        if _stored_in_collection(self, owner):
+            list_.appendleft(self._listen_fn)
+            return True
+        else:
+            return False

test/base/test_events.py

@@ -996,6 +996,25 @@ class RemovalTest(fixtures.TestBase):
             dispatch = event.dispatcher(TargetEvents)
         return Target
 
+    def _wrapped_fixture(self):
+        class TargetEvents(event.Events):
+            @classmethod
+            def _listen(cls, event_key):
+                fn = event_key.fn
+
+                def adapt(value):
+                    fn("adapted " + value)
+                event_key = event_key.with_wrapper(adapt)
+
+                event_key.base_listen()
+
+            def event_one(self, value):
+                pass
+
+        class Target(object):
+            dispatch = event.dispatcher(TargetEvents)
+        return Target
+
     def test_clslevel(self):
         Target = self._fixture()
 
@@ -1194,3 +1213,43 @@ class RemovalTest(fixtures.TestBase):
             "deque mutated during iteration",
             t1.dispatch.event_one
         )
+
+    def test_double_event_nonwrapped(self):
+        Target = self._fixture()
+
+        listen_one = Mock()
+        t1 = Target()
+        event.listen(t1, "event_one", listen_one)
+        event.listen(t1, "event_one", listen_one)
+
+        t1.dispatch.event_one("t1")
+
+        # doubles are eliminated
+        eq_(listen_one.mock_calls, [call("t1")])
+
+        # only one remove needed
+        event.remove(t1, "event_one", listen_one)
+        t1.dispatch.event_one("t2")
+
+        eq_(listen_one.mock_calls, [call("t1")])
+
+    def test_double_event_wrapped(self):
+        # this is issue #3199
+        Target = self._wrapped_fixture()
+
+        listen_one = Mock()
+        t1 = Target()
+
+        event.listen(t1, "event_one", listen_one)
+        event.listen(t1, "event_one", listen_one)
+
+        t1.dispatch.event_one("t1")
+
+        # doubles are eliminated
+        eq_(listen_one.mock_calls, [call("adapted t1")])
+
+        # only one remove needed
+        event.remove(t1, "event_one", listen_one)
+        t1.dispatch.event_one("t2")
+
+        eq_(listen_one.mock_calls, [call("adapted t1")])