fields.py 文件源码

def contribute_to_class(self, cls, name, **kwargs):
        if not self.sorted:
            return super(SortedManyToManyField, self).contribute_to_class(cls, name, **kwargs)

        # To support multiple relations to self, it's useful to have a non-None
        # related name on symmetrical relations for internal reasons. The
        # concept doesn't make a lot of sense externally ("you want me to
        # specify *what* on my non-reversible relation?!"), so we set it up
        # automatically. The funky name reduces the chance of an accidental
        # clash.
        if self.rel.symmetrical and (self.rel.to == "self" or self.rel.to == cls._meta.object_name):
            self.rel.related_name = "%s_rel_+" % name

        super(ManyToManyField, self).contribute_to_class(cls, name, **kwargs)

        # The intermediate m2m model is not auto created if:
        #  1) There is a manually specified intermediate, or
        #  2) The class owning the m2m field is abstract.
        if not self.rel.through and not cls._meta.abstract:
            self.rel.through = self.create_intermediate_model(cls)

        # Add the descriptor for the m2m relation
        setattr(cls, self.name, SortedManyToManyDescriptor(self))

        # Set up the accessor for the m2m table name for the relation
        self.m2m_db_table = curry(self._get_m2m_db_table, cls._meta)

        # Populate some necessary rel arguments so that cross-app relations
        # work correctly.
        if isinstance(self.rel.through, six.string_types):
            def resolve_through_model(field, model, cls):
                field.rel.through = model
            add_lazy_relation(cls, self, self.rel.through, resolve_through_model)

        if hasattr(cls._meta, 'duplicate_targets'):  # Django<1.5
            if isinstance(self.rel.to, six.string_types):
                target = self.rel.to
            else:
                target = self.rel.to._meta.db_table
            cls._meta.duplicate_targets[self.column] = (target, "m2m")