django 的model是如何把字段加入到meta中的

def contribute_to_class(self, cls, name): ???????self.set_attributes_from_name(name) ???????self.model = cls ???????cls._meta.add_field(self) ???????if self.choices: ???????????setattr(cls, ‘get_%s_display‘ % self.name, ???????????????????curry(cls._get_FIELD_display, field=self))

def add_field(self, field): ???????# Insert the given field in the order in which it was created, using ???????# the "creation_counter" attribute of the field. ???????# Move many-to-many related fields from self.fields into ???????# self.many_to_many. ???????if field.rel and isinstance(field.rel, ManyToManyRel): ???????????self.local_many_to_many.insert(bisect(self.local_many_to_many, field), field) ???????????if hasattr(self, ‘_m2m_cache‘): ???????????????del self._m2m_cache ???????else: ???????????self.local_fields.insert(bisect(self.local_fields, field), field) ???????????self.setup_pk(field) ???????????if hasattr(self, ‘_field_cache‘): ???????????????del self._field_cache ???????????????del self._field_name_cache ???????if hasattr(self, ‘_name_map‘): ???????????del self._name_map

fields = property(_fields) ???def get_fields_with_model(self): ???????""" ???????Returns a sequence of (field, model) pairs for all fields. The "model" ???????element is None for fields on the current model. Mostly of use when ???????constructing queries so that we know which model a field belongs to. ???????""" ???????try: ???????????self._field_cache ???????except AttributeError: ???????????self._fill_fields_cache() ???????return self._field_cache ???def _fill_fields_cache(self): ???????cache = [] ???????for parent in self.parents: ???????????for field, model in parent._meta.get_fields_with_model(): ???????????????if model: ???????????????????cache.append((field, model)) ???????????????else: ???????????????????cache.append((field, parent)) ???????cache.extend([(f, None) for f in self.local_fields]) ???????self._field_cache = tuple(cache) ???????self._field_name_cache = [x for x, _ in cache]