event listener not working for sessionmaker, or any Session subclass

[Mike Bayer]

import sqlalchemy as sa
import sqlalchemy.exc as saexc
import sqlalchemy.ext.declarative as sadec
import sqlalchemy.sql as sasql
import sqlalchemy.orm as saorm

@sa.event.listens_for(saorm.Session, 'before_flush')
def handler1(session, flush_context, instances):
    print 'handler1'

engine = sa.create_engine('sqlite://')
meta = sa.MetaData()
Base = sadec.declarative_base(metadata=meta)

class MySession(saorm.Session):
    pass

# works
#sess = saorm.Session(bind=engine, autoflush=False)

# fails
#sessmaker = saorm.sessionmaker(bind = engine, autoflush = False)
#sess = sessmaker()

# fails
sess = MySession(bind=engine, autoflush=False)

class Anything(Base):
    __tablename__ = 'families'

    id = sa.Column(sa.Integer, primary_key=True)

meta.create_all(bind=engine)

@sa.event.listens_for(saorm.Session, 'before_flush')
def handler2(session, flush_context, instances):
    print 'handler2'

f = Anything()
sess.add(f)
sess.commit()

[Mike Bayer]

this is basically an issue with class generation in the event system.

[Mike Bayer]

this is not the fix but illustrates the issue, that new subclasses made after the fact don't get populated in the parent._clslevel mapping.

diff -r be71c73f614f9c316c0c02a98505a8c03d5ef788 lib/sqlalchemy/event.py
--- a/lib/sqlalchemy/event.py   Mon Mar 05 15:20:07 2012 -0500
+++ b/lib/sqlalchemy/event.py   Wed Mar 07 11:28:21 2012 -0500
@@ -252,11 +252,20 @@
     _exec_once = False

     def __init__(self, parent, target_cls):
-        self.parent_listeners = parent._clslevel[target_cls](target_cls)
+        #self.parent_listeners = parent._clslevel[target_cls](target_cls)
+        self.target_cls = target_cls
+        self.parent = parent
         self.name = parent.__name__
         self.listeners = [        self.propagate = set()

+    @property
+    def parent_listeners(self):
+        lis = set()
+        for cls in self.target_cls.__mro__:
+            lis.update(self.parent._clslevel[cls](]
))
+        return list(lis)
+
     def exec_once(self, *args, **kw):
         """Execute this event, but only if it has not been
         executed already for this collection."""

[Mike Bayer]

here's a patch that fixes, though we're having a heisenbug in test.sql.test_metadata:CatchAllEventsTest with it. Running test_metadata by itself passes, running all of -w sql, the patch fails, so something with the "event cleanup" code might be getting in the way here.

diff -r be71c73f614f9c316c0c02a98505a8c03d5ef788 lib/sqlalchemy/event.py
--- a/lib/sqlalchemy/event.py   Mon Mar 05 15:20:07 2012 -0500
+++ b/lib/sqlalchemy/event.py   Wed Mar 07 11:54:00 2012 -0500
@@ -206,21 +206,19 @@
         assert isinstance(target, type), \
                 "Class-level Event targets must be classes."

-        stack = [target](target)
-        while stack:
-            cls = stack.pop(0)
-            stack.extend(cls.__subclasses__())
-            self._clslevel[cls](cls).insert(0, obj)
+        self._clslevel[target](target).insert(0, obj)

     def append(self, obj, target, propagate):
         assert isinstance(target, type), \
                 "Class-level Event targets must be classes."

-        stack = [target](target)
-        while stack:
-            cls = stack.pop(0)
-            stack.extend(cls.__subclasses__())
-            self._clslevel[cls](cls).append(obj)
+        self._clslevel[target](target).append(obj)
+
+    def update_subclass(self, target):
+        clslevel = self._clslevel[target](target)
+        for cls in target.__mro__:
+            if cls in self._clslevel:
+                clslevel.extend(self._clslevel[cls](cls))

     def remove(self, obj, target):
         stack = [target](target)
@@ -252,6 +250,8 @@
     _exec_once = False

     def __init__(self, parent, target_cls):
+        if target_cls not in parent._clslevel:
+            parent.update_subclass(target_cls)
         self.parent_listeners = parent._clslevel[target_cls](target_cls)
         self.name = parent.__name__
         self.listeners = []

[Mike Bayer]

yeah it's the "clear" - which needs to hold onto those lists that are already created. if we just make that check for parent._cls more liberal then it's OK:

diff -r be71c73f614f9c316c0c02a98505a8c03d5ef788 lib/sqlalchemy/event.py
--- a/lib/sqlalchemy/event.py   Mon Mar 05 15:20:07 2012 -0500
+++ b/lib/sqlalchemy/event.py   Wed Mar 07 11:59:36 2012 -0500
@@ -206,21 +206,19 @@
         assert isinstance(target, type), \
                 "Class-level Event targets must be classes."

-        stack = [target](target)
-        while stack:
-            cls = stack.pop(0)
-            stack.extend(cls.__subclasses__())
-            self._clslevel[cls](cls).insert(0, obj)
+        self._clslevel[target](target).insert(0, obj)

     def append(self, obj, target, propagate):
         assert isinstance(target, type), \
                 "Class-level Event targets must be classes."

-        stack = [target](target)
-        while stack:
-            cls = stack.pop(0)
-            stack.extend(cls.__subclasses__())
-            self._clslevel[cls](cls).append(obj)
+        self._clslevel[target](target).append(obj)
+
+    def update_subclass(self, target):
+        clslevel = self._clslevel[target](target)
+        for cls in target.__mro__:
+            if cls in self._clslevel:
+                clslevel.extend(self._clslevel[cls](cls))

     def remove(self, obj, target):
         stack = [target](target)
@@ -252,6 +250,8 @@
     _exec_once = False

     def __init__(self, parent, target_cls):
+        if not parent._clslevel[target_cls](target_cls):
+            parent.update_subclass(target_cls)
         self.parent_listeners = parent._clslevel[target_cls](target_cls)
         self.name = parent.__name__
         self.listeners = []

this incurs a lot of unnecessary, instance-level calls to update_subclass() though, in the usual case that there's no events set up, so let's keep trying

[Mike Bayer]

this one should do it:

diff -r be71c73f614f9c316c0c02a98505a8c03d5ef788 lib/sqlalchemy/event.py
--- a/lib/sqlalchemy/event.py   Mon Mar 05 15:20:07 2012 -0500
+++ b/lib/sqlalchemy/event.py   Wed Mar 07 12:13:36 2012 -0500
@@ -210,7 +210,11 @@
         while stack:
             cls = stack.pop(0)
             stack.extend(cls.__subclasses__())
-            self._clslevel[cls](cls).insert(0, obj)
+            if cls is not target and \
+                cls not in self._clslevel:
+                self.update_subclass(cls)
+            else:
+                self._clslevel[cls](cls).insert(0, obj)

     def append(self, obj, target, propagate):
         assert isinstance(target, type), \
@@ -220,7 +224,18 @@
         while stack:
             cls = stack.pop(0)
             stack.extend(cls.__subclasses__())
-            self._clslevel[cls](cls).append(obj)
+            if cls is not target and \
+                cls not in self._clslevel:
+                self.update_subclass(cls)
+            else:
+                self._clslevel[cls](cls).append(obj)
+
+
+    def update_subclass(self, target):
+        clslevel = self._clslevel[target](target)
+        for cls in target.__mro__:
+            if cls in self._clslevel:
+                clslevel.extend(self._clslevel[cls](cls))

     def remove(self, obj, target):
         stack = [target](target)
@@ -252,6 +267,8 @@
     _exec_once = False

     def __init__(self, parent, target_cls):
+        if target_cls not in parent._clslevel:
+            parent.update_subclass(target_cls)
         self.parent_listeners = parent._clslevel[target_cls](target_cls)
         self.name = parent.__name__
         self.listeners = []

[Mike Bayer]

8696a45b096dd7fedb6e9683bef4de99220c976d

[Mike Bayer]

Removing milestone: 0.7.6 (automated comment)