first take at backreference handlers

1 files changed, 44 insertions, 2 deletions

diff --git a/lib/sqlalchemy/attributes.py b/lib/sqlalchemy/attributes.py
index aa768532d..9bdfcab6a 100644
--- a/lib/sqlalchemy/attributes.py
+++ b/lib/sqlalchemy/attributes.py
@@ -44,10 +44,11 @@ class PropHistory(object):
     """manages the value of a particular scalar attribute on a particular object instance."""
     # make our own NONE to distinguish from "None"
     NONE = object()
-    def __init__(self, obj, key, **kwargs):
+    def __init__(self, obj, key, backrefmanager=None, **kwargs):
         self.obj = obj
         self.key = key
         self.orig = PropHistory.NONE
+        self.backrefmanager = backrefmanager
     def gethistory(self, *args, **kwargs):
         return self
     def history_contains(self, obj):
@@ -61,9 +62,13 @@ class PropHistory(object):
             raise ("assigning a list to scalar property '%s' on '%s' instance %d" % (self.key, self.obj.__class__.__name__, id(self.obj)))
         self.orig = self.obj.__dict__.get(self.key, None)
         self.obj.__dict__[self.key] = value
+        if self.backrefmanager is not None and self.orig is not value:
+            self.backrefmanager.set(self.obj, value, self.orig)
     def delattr(self):
         self.orig = self.obj.__dict__.get(self.key, None)
         self.obj.__dict__[self.key] = None
+        if self.backrefmanager is not None:
+            self.backrefmanager.set(self.obj, None, self.orig)
     def rollback(self):
         if self.orig is not PropHistory.NONE:
             self.obj.__dict__[self.key] = self.orig
@@ -88,9 +93,10 @@ class PropHistory(object):
 
 class ListElement(util.HistoryArraySet):
     """manages the value of a particular list-based attribute on a particular object instance."""
-    def __init__(self, obj, key, data=None, **kwargs):
+    def __init__(self, obj, key, data=None, backrefmanager=None, **kwargs):
         self.obj = obj
         self.key = key
+        self.backrefmanager = backrefmanager
         # if we are given a list, try to behave nicely with an existing
         # list that might be set on the object already
         try:
@@ -120,11 +126,15 @@ class ListElement(util.HistoryArraySet):
         res = util.HistoryArraySet._setrecord(self, item)
         if res:
             self.list_value_changed(self.obj, self.key, item, self, False)
+            if self.backrefmanager is not None:
+                self.backrefmanager.append(self.obj, item)
         return res
     def _delrecord(self, item):
         res = util.HistoryArraySet._delrecord(self, item)
         if res:
             self.list_value_changed(self.obj, self.key, item, self, True)
+            if self.backrefmanager is not None:
+                self.backrefmanager.delete(self.obj, item)
         return res
 
 class CallableProp(object):
@@ -175,6 +185,38 @@ class CallableProp(object):
     def rollback(self):
         pass
 
+class BackrefManager(object):
+    def __init__(self, key):
+        self.key = key
+    def append(self, parent, child):
+        pass
+    def delete(self, parent, child):
+        pass
+    def set(self, parent, child, oldchild):
+        pass
+
+
+class ListBackrefManager(BackrefManager):
+    def append(self, parent, child):
+        getattr(child, self.key).append(parent)
+    def delete(self, parent, child):
+        getattr(child, self.key).remove(parent)
+
+class OneToManyBackrefManager(BackrefManager):
+    def append(self, parent, child):
+        setattr(child, self.key, parent)
+    def delete(self, parent, child):
+        setattr(child, self.key, None)
+
+class ManyToOneBackrefManager(BackrefManager):
+    def set(self, parent, child, oldchild):
+        if oldchild is not None:
+            try:
+                getattr(oldchild, self.key).remove(parent)
+            except:
+                print "wha? oldchild is ", repr(oldchild)
+        if child is not None:
+            getattr(child, self.key).append(parent)
             
 class AttributeManager(object):
     """maintains a set of per-attribute callable/history manager objects for a set of objects."""