Question

I have this “jobs” model (shown below).

• There is a M2M relationship between Hosts and Locations(A location has multiple hosts assigned to it).
• I also have a Timezone class with a Foreign Key relationship defined between location and timezone(A location is assigned a timezone)

The problem I’m having is that i cannot un-comment the ‘colo’ item in the Host class because of the foreign key reference to “Location”. The Location class is defined after the Host class. But i cannot move the definition of the Location to above the Host class because of the M2M reference for “hosts” in the Location class.

Am i missing something conceptually? Any help would be greatly appreciated!

Here is the relevant part of my model:

class Timezone(models.Model):
    name = models.CharField(max_length=32, unique=True)
    def __unicode__(self):
        return "%s"%(self.name)

class Host(models.Model):
    name = models.CharField(max_length=32, unique=True)
#    colo = models.ForeignKey(Location)
    def __unicode__(self):
        return "%s"%(self.name)

class Location(models.Model):
    name = models.CharField(max_length=3, unique=True)
    hosts = models.ManyToManyField(Host, blank=True) #not required
    tz = models.ForeignKey(Timezone)
    def __unicode__(self):
        return "%s"%(self.name)

Answer 1

Since a Host will only ever have one location, you can remove the locations field from the host model, or remove colo, and change locations to location = models.ForeignKey(Location)

To get all hosts from a location, you can do

location = Location.objects.get(pk=1)
hosts = location.host_set.all() #returns all hosts for the location

Here’s a link to the Django docs about backwards relationships