Python django.db.models.fields.related 模块，ManyToOneRel() 实例源码

def check_reverse_relation(model, related_name):
    """
        Helper method to check if a given model related_name pair return a
        reverse relation instance that is associated by a ForeignKey.

        model: subclass of django.db.models.Model
        related_name: str
    """
    rel = get_reverse_relation(model, related_name)
    if rel is None:
        raise NotImplementedError(
            '{} does not have a reverse relation by the name "{}"'.format(
                model.__name__, related_name
            )
        )
    elif not isinstance(rel, ManyToOneRel):
        raise TypeError(
            'The reverse relation "{}" on {}.{} is not a ForeignKey.'
            'Timeseries only works with ForeignKey reverse relations.'.format(
                related_name, rel.field.model.__name__, rel.field.name
            )
        )

    return rel

def is_valid_field(self, model, field):
        """
        Return true if the field exists within the model (or in the related
        model specified using the Django ORM __ notation)
        """
        components = field.split('__', 1)
        try:
            field, _parent_model, _direct, _m2m = \
                model._meta.get_field_by_name(components[0])

            # reverse relation
            if isinstance(field, _RelatedObject):
                return self.is_valid_field(field.model, components[1])

            # foreign key
            if field.rel and len(components) == 2:
                return self.is_valid_field(field.rel.to, components[1])
            return True
        except FieldDoesNotExist:
            return False

def serializer_factory(endpoint=None, fields=None, base_class=None, model=None):

    if model is not None:
        assert endpoint is None, "You cannot specify both a model and an endpoint"
        from .endpoints import Endpoint
        endpoint = Endpoint(model=model)
    else:
        assert endpoint is not None, "You have to specify either a model or an endpoint"

    if base_class is None:
        base_class = endpoint.base_serializer

    meta_attrs = {
        'model': endpoint.model,
        'fields': fields if fields is not None else endpoint.get_fields_for_serializer()
    }
    meta_parents = (object, )
    if hasattr(base_class, 'Meta'):
        meta_parents = (base_class.Meta, ) + meta_parents

    Meta = type('Meta', meta_parents, meta_attrs)

    cls_name = '{}Serializer'.format(endpoint.model.__name__)
    cls_attrs = {
        'Meta': Meta,
    }

    for meta_field in meta_attrs['fields']:
        if meta_field not in base_class._declared_fields:
            try:
                model_field = endpoint.model._meta.get_field(meta_field)
                if isinstance(model_field, OneToOneRel):
                    cls_attrs[meta_field] = serializers.PrimaryKeyRelatedField(read_only=True)
                elif isinstance(model_field, ManyToOneRel):
                    cls_attrs[meta_field] = serializers.PrimaryKeyRelatedField(many=True, read_only=True)
            except FieldDoesNotExist:
                cls_attrs[meta_field] = serializers.ReadOnlyField()

    return type(cls_name, (NullToDefaultMixin, base_class, ), cls_attrs)

def get_field_names(model):
    '''Return a List of all fieldnames from a given model as strings sorted alphabetically.'''
    return sorted([f.name for f in model._meta.get_fields()  # noqa
                   if not isinstance(f, ManyToOneRel)])