Return the name of the related model, as used to store all models in the
        database object, in the following format: "%(namespace)s:%(class_name)"
        The result is computed from the "to" argument of the RelatedField
        constructor, stored in the "related_to" attribute, based on theses rules :
        - if a "RelatedModel" subclass, get its namespace:name
        - if a string :
          - if "self", get from the current model (relation on self)
          - if a RelatedModel class name, keep it, and if no namesace, use the
            namespace of the current model

def _get_related_model_name(self):
        """
        Return the name of the related model, as used to store all models in the
        database object, in the following format: "%(namespace)s:%(class_name)"
        The result is computed from the "to" argument of the RelatedField
        constructor, stored in the "related_to" attribute, based on theses rules :
        - if a "RelatedModel" subclass, get its namespace:name
        - if a string :
          - if "self", get from the current model (relation on self)
          - if a RelatedModel class name, keep it, and if no namesace, use the
            namespace of the current model
        """
        if isinstance(self.related_to, type) and issubclass(self.related_to, RelatedModel):
            model_name = self.related_to._name

        elif isinstance(self.related_to, str):
            if self.related_to == 'self':
                model_name = self._model._name
            elif ':' not in self.related_to:
                model_name = ':'.join((self._model.namespace, self.related_to))
            else:
                model_name = self.related_to

        else:
            raise ImplementationError("The `to` argument to a related field "
                                      "must be a RelatedModel as a class or as "
                                      "a string (with or without namespace). "
                                      "Or simply 'self'.")

        return model_name.lower()