from django.db import models class Building(models.Model): name = models.CharField(max_length=10) def __unicode__(self): return u"Building: %s" % self.name class Device(models.Model): building = models.ForeignKey('Building') name = models.CharField(max_length=10) def __unicode__(self): return u"device '%s' in building %s" % (self.name, self.building) class Port(models.Model): device = models.ForeignKey('Device') port_number = models.CharField(max_length=10) def __unicode__(self): return u"%s/%s" % (self.device.name, self.port_number) class Connection(models.Model): start = models.ForeignKey(Port, related_name='connection_start', unique=True) end = models.ForeignKey(Port, related_name='connection_end', unique=True) def __unicode__(self): return u"%s to %s" % (self.start, self.end) __test__ = {'API_TESTS': """ Regression test for bug #7110. When using select_related(), we must query the Device and Building tables using two different aliases (each) in order to differentiate the start and end Connection fields. The net result is that both the "connections = ..." queries here should give the same results. >>> b=Building.objects.create(name='101') >>> dev1=Device.objects.create(name="router", building=b) >>> dev2=Device.objects.create(name="switch", building=b) >>> dev3=Device.objects.create(name="server", building=b) >>> port1=Port.objects.create(port_number='4',device=dev1) >>> port2=Port.objects.create(port_number='7',device=dev2) >>> port3=Port.objects.create(port_number='1',device=dev3) >>> c1=Connection.objects.create(start=port1, end=port2) >>> c2=Connection.objects.create(start=port2, end=port3) >>> connections=Connection.objects.filter(start__device__building=b, end__device__building=b).order_by('id') >>> [(c.id, unicode(c.start), unicode(c.end)) for c in connections] [(1, u'router/4', u'switch/7'), (2, u'switch/7', u'server/1')] >>> connections=Connection.objects.filter(start__device__building=b, end__device__building=b).select_related().order_by('id') >>> [(c.id, unicode(c.start), unicode(c.end)) for c in connections] [(1, u'router/4', u'switch/7'), (2, u'switch/7', u'server/1')] # This final query should only join seven tables (port, device and building # twice each, plus connection once). >>> connections.query.count_active_tables() 7 """}