Enable pickling of Django QuerySet with abstract intermediate model

fields.py

import copy_reg


from django.db.models.fields import Field, _load_field, _empty

def _load_field_for_abstract(model, field_name):
    return model._meta.get_field(field_name)



def pickle_abstract_field(field):
    """
    Pickling should return the model._meta.fields instance of the field,
    not a new copy of that field. So, we use the app registry to load the
    model and then the field back.
    """

    self = field
    if not hasattr(self, 'model'):
        # Fields are sometimes used without attaching them to models (for
        # example in aggregation). In this case give back a plain field
        # instance. The code below will create a new empty instance of
        # class self.__class__, then update its dict with self.__dict__
        # values - so, this is very close to normal pickle.
        return _empty, (self.__class__,), self.__dict__
    if self.model._deferred:
        # Deferred model will not be found from the app registry. This
        # could be fixed by reconstructing the deferred model on unpickle.
        raise RuntimeError("Fields of deferred models can't be reduced")
    if self.model._meta.abstract:
        func = _load_field_for_abstract
        args = (
            self.model,
            self.name
        )
    else:
        func = _load_field
        args = (
            self.model._meta.app_label, self.model._meta.object_name,
            self.name
        )
    return func, args

copy_reg.pickle(Field, pickle_abstract_field)