Enable django-piston to POST/PUT models with ForeignKeys

django-piston POSTPUT

	def flatten_dict(self, dct):
		out = {}
		for field in dct.keys():
			fk = self.model._meta.get_field(field)
			if isinstance(fk, ForeignKey):
				# Determine the target model of the ForeignKey
				Klass = fk.rel.to().__class__
				d  = { Klass._meta.pk.name : dct[field] }
				# Grab the instance
				i = Klass.objects.get(**d)

				out[field] = i
			else:
				out[field] = dct[field]

		return out