Give `populate_from` callables access to model instances

[willhardy]

It's useful to have access to the model instance when providing a default value in a populate_from function.

The documentation for this should point out that it's often better to put this logic in the database, using model class linked metadata and template variables.

I imagine it would be best to require all populate_from functions to accept any arguments provided, by using the **kwargs parameter. The system can then provide model_instance, view_name, model_class or whatever else the relevant backend has available. This will help futureproof implementations using the seo library.

[willhardy]

Closed by bf1972b. Model instance available to populate_from methods.

[blite]

this doesn't seem to be fully fixed for me

on the example http://django-seo.readthedocs.org/en/latest/reference/definition.html#all-fields

def default_title(metadata, model_instance=None, **kwargs):
if model_instance:
return "My Website: %s" % model_instance.name
else:
return None

doesn't work for me, but

def default_title(metadata, model_instance=None, **kwargs):
    if model_instance:
        return "My Website: %s" % model_instance._content_object.name
    else:
        return None  

does work

i'm guessing the error is in this:

        def _process_context(self, context):
            context['content_type'] = self._content_type
            context['model_instance'] = self