magic-removal: Added ReverseManyRelatedObjectsDescriptor, which implements many-to-many lookup -- e.g. poll_obj.sites rather than poll_obj.get_site_list(). Many-to-many addition/deletion still needs to be done.

git-svn-id: http://code.djangoproject.com/svn/django/branches/magic-removal@2247 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/base.py

@@ -357,22 +357,6 @@ class Model(object):
             setattr(self, cachename, get_image_dimensions(filename))
         return getattr(self, cachename)
 
-    def _get_many_to_many_objects(self, field_with_rel):
-        cache_var = '_%s_cache' % field_with_rel.name
-        if not hasattr(self, cache_var):
-            rel_opts = field_with_rel.rel.to._meta
-            sql = "SELECT %s FROM %s a, %s b WHERE a.%s = b.%s AND b.%s = %%s %s" % \
-                (','.join(['a.%s' % backend.quote_name(f.column) for f in rel_opts.fields]),
-                backend.quote_name(rel_opts.db_table),
-                backend.quote_name(field_with_rel.get_m2m_db_table(self._meta)),
-                backend.quote_name(rel_opts.pk.column),
-                backend.quote_name(rel_opts.object_name.lower() + '_id'),
-                backend.quote_name(self._meta.object_name.lower() + '_id'), rel_opts.get_order_sql('a'))
-            cursor = connection.cursor()
-            cursor.execute(sql, [self._get_pk_val()])
-            setattr(self, cache_var, [field_with_rel.rel.to(*row) for row in cursor.fetchall()])
-        return getattr(self, cache_var)
-
     def _set_many_to_many_objects(self, id_list, field_with_rel):
         current_ids = [obj._get_pk_val() for obj in self._get_many_to_many_objects(field_with_rel)]
         ids_to_add, ids_to_delete = dict([(i, 1) for i in id_list]), []

django/db/models/fields/related.py

@@ -1,3 +1,4 @@
+from django.db import backend
 from django.db.models import signals
 from django.db.models.fields import AutoField, Field, IntegerField
 from django.db.models.related import RelatedObject
@@ -126,14 +127,59 @@ class ManyRelatedObjectsDescriptor(object):
 
         # Prepare the manager.
         # TODO: Fix this hack?
-        # We're setting self.manager.model here because
+        # We're setting manager.model here because manager._prepare() expects
-        # self.manager._prepare() expects that self.manager.model is
+        # that manager.model is set. This is slightly hackish.
-        # set. This is slightly hackish.
         manager.model = self.related.model
         manager._prepare()
 
         return manager
 
+class ReverseManyRelatedObjectsDescriptor(object):
+    # This class provides the functionality that makes the related-object
+    # managers available as attributes on a model class, for fields that have
+    # multiple "remote" values and have a ManyToManyField defined in their
+    # model (rather than having another model pointed *at* them).
+    # In the example "poll.sites", the sites attribute is a
+    # ManyRelatedObjectsDescriptor instance.
+    def __init__(self, m2m_field):
+        self.field = m2m_field
+        self.rel_model = m2m_field.rel.to
+
+    def __get__(self, instance, instance_type=None):
+        if instance is None:
+            raise AttributeError, "Manager must be accessed via instance"
+
+        qn = backend.quote_name
+        this_opts = instance.__class__._meta
+        rel_opts = self.rel_model._meta
+        join_table = backend.quote_name(self.field.get_m2m_db_table(this_opts))
+
+        # Dynamically create a class that subclasses the related
+        # model's default manager.
+        superclass = self.rel_model._default_manager.__class__
+        class_ = types.ClassType('RelatedManager', (superclass,), {})
+        # Override get_query_set on the RelatedManager
+        def get_query_set(self):
+            return superclass.get_query_set(self).extra(
+                tables=(join_table,),
+                where=[
+                    '%s.%s = %s.%s' % (qn(rel_opts.db_table), qn(rel_opts.pk.column), join_table, rel_opts.object_name.lower() + '_id'),
+                    '%s.%s = %%s' % (join_table, this_opts.object_name.lower() + '_id')
+                ],
+                params = [instance._get_pk_val()]
+            )
+        class_.get_query_set = get_query_set
+        manager = class_()
+
+        # Prepare the manager.
+        # TODO: Fix this hack?
+        # We're setting manager.model here because manager._prepare() expects
+        # that manager.model is set. This is slightly hackish.
+        manager.model = self.rel_model
+        manager._prepare()
+
+        return manager
+
 class ForeignKey(RelatedField, Field):
     empty_strings_allowed = False
     def __init__(self, to, to_field=None, **kwargs):
@@ -336,9 +382,7 @@ class ManyToManyField(RelatedField, Field):
 
     def contribute_to_class(self, cls, name):
         super(ManyToManyField, self).contribute_to_class(cls, name)
-        # Add "get_thingie" methods for many-to-many related objects.
+        setattr(cls, self.name, ReverseManyRelatedObjectsDescriptor(self))
-        # EXAMPLES: Poll.get_site_list(), Story.get_byline_list()
-        setattr(cls, 'get_%s_list' % self.rel.singular, curry(cls._get_many_to_many_objects, field_with_rel=self))
 
         # Add "set_thingie" methods for many-to-many related objects.
         # EXAMPLES: Poll.set_sites(), Story.set_bylines()