[1.7.x] Fixed #22351 -- Removed usage of lambdas in model field options.

reference to the same instance of that object would be used as the default

value in all new model instances. Instead, wrap the desired default in a

callable.  For example, if you had a custom ``JSONField`` and wanted to specify

a dictionary as the default, use a ``lambda`` as follows::

a dictionary as the default, use a function as follows::

    contact_info = JSONField("ContactInfo", default=lambda:{"email": "to1@example.com"})

    def contact_default():

        return {"email": "to1@example.com"}

    contact_info = JSONField("ContactInfo", default=contact_default)

Note that ``lambda``\s cannot be used for field options like ``default``

because they cannot be :ref:`serialized by migrations <migration-serializing>`.

See that documentation for other caveats.

``editable``

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

    with the Python ``datetime`` module to limit selections by date range. For

    example::

        limit_choices_to = lambda: {'pub_date__lte': datetime.date.utcnow()}

        def limit_pub_date_choices():

            return {'pub_date__lte': datetime.date.utcnow()}

        limit_choices_to = limit_pub_date_choices

    If ``limit_choices_to`` is or returns a :class:`Q object

    <django.db.models.Q>`, which is useful for :ref:`complex queries