models.py 文件源码

def seed_identifier(cls):  # @NoSelf
        '''returns data_identifier if the latter is not None, else net.sta.loc.cha by querying the
        relative channel and station'''
        # Needed note: To know what we are doing in 'sel' below, please look:
        # http://docs.sqlalchemy.org/en/latest/orm/extensions/hybrid.html#correlated-subquery-relationship-hybrid
        # Notes
        # - we use limit(1) cause we might get more than one
        # result. Regardless of why it happens (because we don't join or apply a distinct?)
        # it is relevant for us to get the first result which has the requested
        # network+station and location + channel strings
        # - the label(...) at the end makes all the difference. The doc is, as always, unclear
        # http://docs.sqlalchemy.org/en/latest/core/sqlelement.html#sqlalchemy.sql.expression.label
        dot = text("'.'")
        sel = select([concat(Station.network, dot, Station.station, dot,
                             Channel.location, dot, Channel.channel)]).\
            where((Channel.id == cls.channel_id) & (Station.id == Channel.station_id)).limit(1).\
            label('seedidentifier')
        return case([(cls.data_identifier.isnot(None), cls.data_identifier)],
                    else_=sel)