Question

I have a Django model with a Person model:

class Person(models.Model):
  # Personal details
  first_name = models.CharField(max_length=50)
  middle_name = models.CharField(max_length=50, blank=True, null=True)
  last_name = models.CharField(max_length=50)
  gender = models.CharField(max_length=1, choices=GENDER_CHOICES)
  date_of_birth = models.DateField()

  # Address
  street_address = models.CharField(max_length=50)
  suburb = models.CharField(max_length=30)
  postcode = models.CharField(max_length=4)
  state = models.CharField(max_length=3, choices=STATE_CHOICES)

  #Contact Details
  email = models.EmailField()

  # Family
  spouse = models.ForeignKey('self', null=True, blank=True)
  children = models.ManyToManyField('self', null=True, blank=True)

  home_church = models.ForeignKey('Church', null=True, blank=True)

The “middle_name” field is nullable, I don’t think there’s any way to avoid that, is there?

However, I also have a nullable ForeignKey for Spouse, a recursive ManyToManyField for their children, and a nullable ForeignKey for church (if relevant).

My question – firstly, what is the current consensus on nullable foreign keys? Should I be allowing it here, or should I be creating some kind of “nobody”, or “unassigned” model to represent not having a spouse/home church?

Or is there some other way that I can rework this design in Django to accommodate for this?

And if I do go ahead with null FK’s, are there any caveats in Django I need to be aware of? (left join?)

Cheers,
Victor

Answer 1

Null is perfectly fine. In python code None will represent Null.

One important thing you should know is that if you delete church, django performs cascading and your Persons from that church will be deleted too. So before deleting church you need to set Null on church field for every person in that church.

Django 1.3 introduces on_delete argument which makes this a lot simper.