def get_instance(self, data):
if self.transient:<EOL><INDENT>return None<EOL><DEDENT>props = get_primary_keys(self.opts.model)<EOL>filters = {prop.key: data.get(prop.key) for prop in props}<EOL>if None not in filters.values():<EOL><INDENT>return self.session.query(self.opts.model).filter_by(**filters).first()<EOL><DEDENT>return None<EOL>
Retrieve an existing record by primary key(s). If the schema instance
        is transient, return None.

        :param data: Serialized data to inform lookup.