--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/parts/django/docs/ref/models/relations.txt	Sat Jan 08 11:20:57 2011 +0530
@@ -0,0 +1,105 @@
+=========================
+Related objects reference
+=========================
+
+.. currentmodule:: django.db.models.fields.related
+
+.. class:: RelatedManager
+
+    A "related manager" is a manager used in a one-to-many or many-to-many
+    related context. This happens in two cases:
+
+        * The "other side" of a :class:`~django.db.models.ForeignKey` relation.
+          That is::
+
+                class Reporter(models.Model):
+                    ...
+
+                class Article(models.Model):
+                    reporter = models.ForeignKey(Reporter)
+
+          In the above example, the methods below will be available on
+          the manager ``reporter.article_set``.
+
+        * Both sides of a :class:`~django.db.models.ManyToManyField` relation::
+
+                class Topping(models.Model):
+                    ...
+
+                class Pizza(models.Model):
+                    toppings = models.ManyToManyField(Topping)
+
+          In this example, the methods below will be available both on
+          ``topping.pizza_set`` and on ``pizza.toppings``.
+
+    These related managers have some extra methods:
+
+    .. method:: add(obj1, [obj2, ...])
+
+        Adds the specified model objects to the related object set.
+
+        Example::
+
+            >>> b = Blog.objects.get(id=1)
+            >>> e = Entry.objects.get(id=234)
+            >>> b.entry_set.add(e) # Associates Entry e with Blog b.
+
+    .. method:: create(**kwargs)
+
+        Creates a new object, saves it and puts it in the related object set.
+        Returns the newly created object::
+
+            >>> b = Blog.objects.get(id=1)
+            >>> e = b.entry_set.create(
+            ...     headline='Hello',
+            ...     body_text='Hi',
+            ...     pub_date=datetime.date(2005, 1, 1)
+            ... )
+
+            # No need to call e.save() at this point -- it's already been saved.
+
+        This is equivalent to (but much simpler than)::
+
+            >>> b = Blog.objects.get(id=1)
+            >>> e = Entry(
+            ...     blog=b,
+            ...     headline='Hello',
+            ...     body_text='Hi',
+            ...     pub_date=datetime.date(2005, 1, 1)
+            ... )
+            >>> e.save(force_insert=True)
+
+        Note that there's no need to specify the keyword argument of the model
+        that defines the relationship. In the above example, we don't pass the
+        parameter ``blog`` to ``create()``. Django figures out that the new
+        ``Entry`` object's ``blog`` field should be set to ``b``.
+
+    .. method:: remove(obj1, [obj2, ...])
+
+        Removes the specified model objects from the related object set::
+
+            >>> b = Blog.objects.get(id=1)
+            >>> e = Entry.objects.get(id=234)
+            >>> b.entry_set.remove(e) # Disassociates Entry e from Blog b.
+
+        In order to prevent database inconsistency, this method only exists on
+        :class:`~django.db.models.ForeignKey` objects where ``null=True``. If
+        the related field can't be set to ``None`` (``NULL``), then an object
+        can't be removed from a relation without being added to another. In the
+        above example, removing ``e`` from ``b.entry_set()`` is equivalent to
+        doing ``e.blog = None``, and because the ``blog``
+        :class:`~django.db.models.ForeignKey` doesn't have ``null=True``, this
+        is invalid.
+
+    .. method:: clear()
+
+        Removes all objects from the related object set::
+
+            >>> b = Blog.objects.get(id=1)
+            >>> b.entry_set.clear()
+
+        Note this doesn't delete the related objects -- it just disassociates
+        them.
+
+        Just like ``remove()``, ``clear()`` is only available on
+        :class:`~django.db.models.ForeignKey`\s where ``null=True``.