properties.py 文件源码

def setup_loader(self, instance):
        def lazyload():
            clause = sql.and_()
            try:
                pk = self.parent.pks_by_table[self.columns[0].table]
            except KeyError:
                pk = self.columns[0].table.primary_key
            for primary_key in pk:
                attr = self.parent._getattrbycolumn(instance, primary_key)
                if not attr:
                    return None
                clause.clauses.append(primary_key == attr)

            if self.group is not None:
                groupcols = [p for p in self.parent.props.values() if isinstance(p, DeferredColumnProperty) and p.group==self.group]
                row = sql.select([g.columns[0] for g in groupcols], clause, use_labels=True).execute().fetchone()
                for prop in groupcols:
                    if prop is self:
                        continue
                    instance.__dict__[prop.key] = row[prop.columns[0]]
                    objectstore.global_attributes.create_history(instance, prop.key, uselist=False)
                return row[self.columns[0]]    
            else:
                return sql.select([self.columns[0]], clause, use_labels=True).scalar()
        return lazyload