Call __del() before remove()

The "remove" event for collections is now called before the item is removed
in the case of the ``collection.remove()`` method, as is consistent with the
behavior for most other forms of collection item removal (such as
``__delitem__``, replacement under ``__setitem__``).  The ``pop()`` methods
are now the only exception as the target item is not available until after
the pop operation proceeds.

This allows ``remove()`` to be consistent in its behavior with all
the other collection operations, allows the "before_delete" hook
to be local to "pop()" operations only, and removes some method overhead.

We are also looking here to gain some more predictability in terms
of the fix for #1103.

Change-Id: I4fdea911517d65cc300fae0e9c351a471e52e4ab

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/attributes.py b/lib/sqlalchemy/orm/attributes.py
index ff730d745..5ba8be439 100644
--- a/lib/sqlalchemy/orm/attributes.py
+++ b/lib/sqlalchemy/orm/attributes.py
@@ -973,6 +973,14 @@ class CollectionAttributeImpl(AttributeImpl):
         return value
 
     def fire_pre_remove_event(self, state, dict_, initiator):
+        """A special event used for pop() operations.
+
+        The "remove" event needs to have the item to be removed passed to
+        it, which in the case of pop from a set, we don't have a way to access
+        the item before the operation.   the event is used for all pop()
+        operations (even though set.pop is the one where it is really needed).
+
+        """
         state._modified_event(dict_, self, NEVER_SET, True)
 
     def fire_remove_event(self, state, dict_, value, initiator):