def get_instance(self, data):
        """Retrieve an existing record by primary key(s). If the schema instance
        is transient, return None.

        :param data: Serialized data to inform lookup.
        """
        if self.transient:
            return None
        props = get_primary_keys(self.opts.model)
        filters = {prop.key: data.get(prop.key) for prop in props}
        if None not in filters.values():
            return self.session.query(self.opts.model).filter_by(**filters).first()
        return None
Retrieve an existing record by primary key(s). If the schema instance
        is transient, return None.

        :param data: Serialized data to inform lookup.