[1.10.x] Fixed #26787 -- Documented deleting and reloading of model instance fields.

Refreshing objects from database

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

If you delete a field from a model instance, accessing it again reloads the

value from the database::

    >>> obj = MyModel.objects.first()

    >>> del obj.field

    >>> obj.field  # Loads the field from the database

.. versionchanged:: 1.10

    In older versions, accessing a deleted field raised ``AttributeError``

    instead of reloading it.

.. method:: Model.refresh_from_db(using=None, fields=None)

If you need to reload a model's values from the database, you can use the

* The ``_base_manager`` and ``_default_manager`` attributes are removed from

  model instances. They remain accessible on the model class.

* Accessing a deleted field on a model instance, e.g. after ``del obj.field``,

  reloads the field's value instead of raising ``AttributeError``.

.. _deprecated-features-1.10:

Features deprecated in 1.10

            # hash)

            hash(Article())

    def test_delete_and_access_field(self):

        # Accessing a field after it's deleted from a model reloads its value.

        pub_date = datetime.now()

        article = Article.objects.create(headline='foo', pub_date=pub_date)

        new_pub_date = article.pub_date + timedelta(days=10)

        article.headline = 'bar'

        article.pub_date = new_pub_date

        del article.headline

        with self.assertNumQueries(1):

            self.assertEqual(article.headline, 'foo')

        # Fields that weren't deleted aren't reloaded.

        self.assertEqual(article.pub_date, new_pub_date)

class ModelLookupTest(TestCase):

    def setUp(self):