queryset-refactor: Added a way to specify the related_name attribute on

abstract base classes.


git-svn-id: http://code.djangoproject.com/svn/django/branches/queryset-refactor@7432 bcc190cf-cafb-0310-a4f2-bffc1f526a37

Author: malcolmt

django/db/models/fields/related.py

@@ -1,3 +1,5 @@
+import copy
+
 from django.db import connection, transaction
 from django.db.models import signals, get_model
 from django.db.models.fields import AutoField, Field, IntegerField, PositiveIntegerField, PositiveSmallIntegerField, get_ul_class
@@ -108,6 +110,8 @@ def contribute_to_class(self, cls, name):
             add_lazy_relation(cls, self, other)
         else:
             self.do_related_class(other, cls)
+        if not cls._meta.abstract and self.rel.related_name:
+            self.rel.related_name = self.rel.related_name % {'class': cls.__name__.lower()}
 
     def set_attributes_from_rel(self):
         self.name = self.name or (self.rel.to._meta.object_name.lower() + '_' + self.rel.to._meta.pk.name)
@@ -149,9 +153,10 @@ def pk_trace(value):
         raise TypeError, "Related Field has invalid lookup: %s" % lookup_type
 
     def _get_related_query_name(self, opts):
-        # This method defines the name that can be used to identify this related object
-        # in a table-spanning query. It uses the lower-cased object_name by default,
-        # but this can be overridden with the "related_name" option.
+        # This method defines the name that can be used to identify this
+        # related object in a table-spanning query. It uses the lower-cased
+        # object_name by default, but this can be overridden with the
+        # "related_name" option.
         return self.rel.related_name or opts.object_name.lower()
 
 class SingleRelatedObjectDescriptor(object):

docs/model-api.txt

@@ -886,13 +886,19 @@ relationship should work. All are optional:
                              `related objects documentation`_ for a full
                              explanation and example.
 
+                             If using this in an `abstract base class`_, be
+                             sure to read the `extra notes`_ in that section
+                             about ``related_name``.
+
     ``to_field``             The field on the related object that the relation
                              is to. By default, Django uses the primary key of
                              the related object.
     =======================  ============================================================
 
 .. _`Database API reference`: ../db-api/
 .. _related objects documentation: ../db-api/#related-objects
+.. _abstract base class: `Abstract base classes`_
+.. _extra notes: `Be careful with related_name`_
 
 Many-to-many relationships
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -2146,6 +2152,39 @@ abstract base class. For example, including ``db_table`` would mean that all
 the child classes (the ones that don't specify their own ``Meta``) would use
 the same database table, which is almost certainly not what you want.
 
+Be careful with ``related_name``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you are using the ``related_name`` attribute on a ``ForeignKey`` or
+``ManyToManyField``, you must always specify a *unique* reverse name for the
+field. This would normally cause a problem in abstract base classes, since the
+fields on this class are included into each of the child classes, with exactly
+the same values for the attributes (including ``related_name``) each time.
+
+To work around this problem, when you are using ``related_name`` in an
+abstract base class (only), part of the name should be the string
+``'%(class)s'``. This is replaced by the lower-cased name of the child class
+that the field is used in. Since each class has a different name, each related
+name will end up being different. For example::
+
+    class Base(models.Model):
+        m2m = models.ManyToMany(OtherModel, related_name="%(class)s_related")
+
+        class Meta:
+            abstract = True
+
+    class ChildA(Base):
+        pass
+
+    class ChildB(Base):
+        pass
+
+The reverse name of the ``ChildA.m2m`` field will be ``childa_related``,
+whilst the reverse name of the ``ChildB.m2m`` field will be
+``childb_related``. It is up to you how you use the ``'%(class)s'`` portion to
+construct your related name, but if you forget to use it, Django will raise
+errors when you validate your models (or run ``syncdb``).
+
 Multi-table inheritance
 -----------------------