django之Model类

Model是model的基类，该类的metaclass是modelbase，在生成model类对象时是采用modelbase的。django.setup()时，apps会把app建立app_config ，知道了每个app的models。每个model类属性_meta是Option类的对象。

field.name为关系field，比如多对多，多对一等。field.attrname为model定义时类变量名称。

@cached_property
    def fields(self):
        """
        Returns a list of all forward fields on the model and its parents,
        excluding ManyToManyFields.

        is_not_an_m2m_field = lambda f: not (f.is_relation and f.many_to_many)
        is_not_a_generic_relation = lambda f: not (f.is_relation and f.one_to_many)
        is_not_a_generic_foreign_key = lambda f: not (
            f.is_relation and f.many_to_one and not (hasattr(f.remote_field, 'model') and f.remote_field.model)
        )
        return make_immutable_fields_list(
            "fields",
            (f for f in self._get_fields(reverse=False) if
            is_not_an_m2m_field(f) and is_not_a_generic_relation(f)
            and is_not_a_generic_foreign_key

def concrete_fields(self):#获取当前model及其父的实体field
        """
        Returns a list of all concrete fields on the model and its parents.

        Private API intended only to be used by Django itself; get_fields()
        combined with filtering of field properties is the public API for
        obtaining this field list.
        """
        return make_immutable_fields_list(
            "concrete_fields", (f for f in self.fields if f.concrete)
        )

    @cached_property
    def local_concrete_fields(self):#获取当前model的实体field
        """
        Returns a list of all concrete fields on the model.

        Private API intended only to be used by Django itself; get_fields()
        combined with filtering of field properties is the public API for
        obtaining this field list.
        """
        return make_immutable_fields_list(
            "local_concrete_fields", (f for f in self.local_fields if f.concrete)
        )

获取model的所有field
def _get_fields(self, forward=True, reverse=True, include_parents=True, include_hidden=False,
                    seen_models=None):
        """
        Internal helper function to return fields of the model.
        * If forward=True, then fields defined on this model are returned.正向，自己的field
        * If reverse=True, then relations pointing to this model are returned.逆向，关联的对象
        * If include_hidden=True, then fields with is_hidden=True are returned.在model隐藏的field
        * The include_parents argument toggles if fields from parent models包括父的field
          should be included. It has three values: True, False, and
          PROXY_PARENTS. When set to PROXY_PARENTS, the call will return all
          fields defined for the current model or any of its parents in the
          parent chain to the model's concrete model.
        """
        if include_parents not in (True, False, PROXY_PARENTS):
            raise TypeError("Invalid argument for include_parents: %s" % (include_parents,))
        # This helper function is used to allow recursion in ``get_fields()``
        # implementation and to provide a fast way for Django's internals to
        # access specific subsets of fields.

        # We must keep track of which models we have already seen. Otherwise we
        # could include the same field multiple times from different models.
        topmost_call = False
        if seen_models is None:
            seen_models = set()
            topmost_call = True
        seen_models.add(self.model)

        # Creates a cache key composed of all arguments
        cache_key = (forward, reverse, include_parents, include_hidden, topmost_call)

        try:
            # In order to avoid list manipulation. Always return a shallow copy
            # of the results.
            return self._get_fields_cache[cache_key]
        except KeyError:
            pass

        fields = []
        # Recursively call _get_fields() on each parent, with the same
        # options provided in this call.
        if include_parents is not False:
            for parent in self.parents:
                # In diamond inheritance it is possible that we see the same
                # model from two different routes. In that case, avoid adding
                # fields from the same parent again.
                if parent in seen_models:
                    continue
                if (parent._meta.concrete_model != self.concrete_model and
                        include_parents == PROXY_PARENTS):
                    continue
                for obj in parent._meta._get_fields(
                        forward=forward, reverse=reverse, include_parents=include_parents,
                        include_hidden=include_hidden, seen_models=seen_models):
                    if hasattr(obj, 'parent_link') and obj.parent_link:#如果field有父link，不加入
                        continue
                    fields.append(obj)
        if reverse:
            # Tree is computed once and cached until the app cache is expired.
            # It is composed of a list of fields pointing to the current model
            # from other models.
            all_fields = self._relation_tree
            for field in all_fields:
                # If hidden fields should be included or the relation is not
                # intentionally hidden, add to the fields dict.
                if include_hidden or not field.remote_field.hidden:
                    fields.append(field.remote_field)#如果远程field不隐藏的话就加入

        if forward:
            fields.extend(
                field for field in chain(self.local_fields, self.local_many_to_many)
            )
            # Virtual fields are recopied to each child model, and they get a
            # different model as field.model in each child. Hence we have to
            # add the virtual fields separately from the topmost call. If we
            # did this recursively similar to local_fields, we would get field
            # instances with field.model != self.model.
            if topmost_call:
                fields.extend(
                    f for f in self.virtual_fields
                )

        # In order to avoid list manipulation. Always
        # return a shallow copy of the results
        fields = make_immutable_fields_list("get_fields()", fields)

        # Store result into cache for later access
        self._get_fields_cache[cache_key] = fields
        return fields