A try of library for defering field in Django. This version is prepared with relationship (FK, ManyToMany etc) in mind. Inpired by https://github.com/mirumee/satchless/blob/master/satchless/util/models.py

Defering Django fields

from django.db import models


class DeferedField(object):
    def __init__(self, cls, **kwargs):
        '''When defining defered field, we declare it's type and properties'''
        self.cls = cls
        self.kwargs = kwargs

    def construct(self, model_alias, **kwargs):
        '''When fixing defered field we give it referenced model
        and may update it's properties'''
        self.kwargs.update(kwargs)
        return self.cls(model_alias, **self.kwargs)


class DeferedForeignKey(DeferedField):
    def __init__(self, **kwargs):
        return super(DeferedField, self).__init__(models.ForeignKey, **kwargs)


class DeferedModel(models.Model):
    class Meta:
        abstract = True

    @classmethod
    def settle(cls, **kwargs):
        new_fields = {}
        # for every class in hierarchy
        # ordered by python's method resoultion order
        for c in reversed(cls.__mro__):
            # inspect all fields of that class
            for field_name, field in c.__dict__.iteritems():
                # to find DeferedField instances
                if isinstance(field, DeferedField):
                    if field_name in kwargs:
                        # and settle them
                        new_fields[field_name] = field.construct(
                                kwargs.pop(field_name))
                    else: # if field_name in kwargs:
                        # or raise error if implementation not given
                        # TODO  fix error class
                        raise TypeError("Implementation of every field is "
                        "required - please profide implementation for %s" %
                        field_name)
        if len(kwargs) > 0:
            # if to many arguments given then probably some error
            raise TypeError("Superficient keyword arguments to sette model")
        # when all field are extracted set them for the class
        for k, v in new_fields.iteritems():
            setattr(c, k, v)
        return cls