Fixed handling of multiple fields in a model pointing to the same related model.

Thanks to ElliotM, mk and oyvind for some excellent test cases for this. Fixed #7110, #7125.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7778 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/options.py

@@ -44,6 +44,7 @@ class Options(object):
         self.one_to_one_field = None
         self.abstract = False
         self.parents = SortedDict()
+        self.duplicate_targets = {}
 
     def contribute_to_class(self, cls, name):
         from django.db import connection
@@ -115,6 +116,24 @@ class Options(object):
                         auto_created=True)
                 model.add_to_class('id', auto)
 
+        # Determine any sets of fields that are pointing to the same targets
+        # (e.g. two ForeignKeys to the same remote model). The query
+        # construction code needs to know this. At the end of this,
+        # self.duplicate_targets will map each duplicate field column to the
+        # columns it duplicates.
+        collections = {}
+        for column, target in self.duplicate_targets.iteritems():
+            try:
+                collections[target].add(column)
+            except KeyError:
+                collections[target] = set([column])
+        self.duplicate_targets = {}
+        for elt in collections.itervalues():
+            if len(elt) == 1:
+                continue
+            for column in elt:
+                self.duplicate_targets[column] = elt.difference(set([column]))
+
     def add_field(self, field):
         # Insert the given field in the order in which it was created, using
         # the "creation_counter" attribute of the field.