Django queryset ManytoMany and OnetoMany

Question

I have this models.py

class Sitename(models.Model): 
   #id              = models.AutoField(primary_key=True)  ## to be removed
    site            = models.CharField()                  ## find values

class Equipment(models.Model):
   #id              = models.AutoField(primary_key=True)  ## to be removed
    serialno        = models.CharField()                  ## known values

class RSL(models.Model): ##Radio Station License
   #id              = models.AutoField(primary_key=True)  ## to be removed
    sitename        = models.ForeignKey(Sitename)
    equipment       = models.ManyToManyField(Equipment)

I only know the Equipment serialno , I can't figure out the proper queryset? So far I know how to query a foreignkey.

sn       = 'abc'

equip    = Equipment.objects.get(serialno=sn)
rsl      = RSL.objects.?????
sitename = Site.objects.get(pk=rsl.pk)

Answer 1

You know the equipment serial no., so use -

equip = Equipment.objects.get(serialno=sn)

Because your equipment field of RSL class and Equipment class are a Many2Many relation, there maybe more than one RSL class objects related to one Equipment object. To get the queryset, use -

rsl_queryset = equip.rsl_set.all()

(Please check whether rsl_set is a method of equip object by checking if it is listed in dir(equip) . Looking at your model, most probably it is. BTW, you can change it to the name you want by adding related_name = "name you want" to the definition. For eg: -

equipment = models.ManyToManyField(Equipment, related_name = "rsl_objects")

This way you can access it by rsl_queryset = equip.rsl_objects.all() )

Now you have got a queryset containing RSL objects related to equip object. So, iterate over them to get the values you want -

for rsl_object in rsl_queryset:
    print "site = " + rsl_object.sitename.site