Added 'Overriding default model methods' section to model-api.txt

.. _Python DB-API: http://www.python.org/peps/pep-0249.html

.. _Other lookup options: http://www.djangoproject.com/documentation/db_api/#extra-params-select-where-tables

Overriding default model methods

--------------------------------

As explained in the `database API docs`_, each model gets a few methods

automatically -- most notably, ``save()`` and ``delete()``. You can override

these methods to alter behavior.

A classic use-case for overriding the built-in methods is if you want something

to happen whenever you save an object. For example::

    class Blog(models.Model):

        name = models.CharField(maxlength=100)

        tagline = models.TextField()

    def save(self):

        do_something()

        super(Blog, self).save() # Call the "real" save() method.

        do_something_else()

You can also prevent saving::

    class Blog(models.Model):

        name = models.CharField(maxlength=100)

        tagline = models.TextField()

    def save(self):

        if self.name == "Yoko Ono's blog":

            return # Yoko shall never have her own blog!

        else:

            super(Blog, self).save() # Call the "real" save() method.

.. _database API docs: http://www.djangoproject.com/documentation/db_api/

Models across files

===================