fields.py 文件源码

def to_mongo(self, document):
        if document is None:
            return None

        if isinstance(document, (dict, SON, ObjectId, DBRef)):
            return document

        id_field_name = document.__class__._meta['id_field']
        id_field = document.__class__._fields[id_field_name]

        if isinstance(document, Document):
            # We need the id from the saved object to create the DBRef
            id_ = document.id
            if id_ is None:
                self.error('You can only reference documents once they have'
                           ' been saved to the database')
        else:
            id_ = document

        id_ = id_field.to_mongo(id_)
        collection = document._get_collection_name()
        ref = DBRef(collection, id_)
        return SON((
            ('_cls', document._class_name),
            ('_ref', ref)
        ))