Question

I have some fields on a model that won’t always be filled in (e.g., the actual completion date and costs until the project is over). Because of this, I thought I’d split the model into two:

1. Model #1: Dense table containing frequently searched and always completed fields
2. Model #2: Sparse table containing infrequently searched and not always completed fields

Questions

1. Am I thinking correctly in splitting this into two models/tables?
2. Should I use Django’s Multi-table Inheritance, or should I explicitly define a OneToOneField? Why?

Configuration

• Django version 1.3.1

Models

Using Django’s Multi-table Inheritance

class Project(models.Model):
    project_number = models.SlugField(max_length=5, blank=False,
            primary_key=True)
    budgeted_costs = models.DecimalField(max_digits=10, decimal_places=2)

class ProjectExtendedInformation(Project):
    submitted_on = models.DateField(auto_now_add=True)
    actual_completion_date = models.DateField(blank=True, null=True)
    actual_project_costs = models.DecimalField(max_digits=10, decimal_places=2,
            blank=True, null=True)

Using an Explicit OneToOneField

class Project(models.Model):
    project_number = models.SlugField(max_length=5, blank=False,
            primary_key=True)
    budgeted_costs = models.DecimalField(max_digits=10, decimal_places=2)

class ProjectExtendedInformation(models.Model):
    project = models.OneToOneField(CapExProject, primary_key=True)
    submitted_on = models.DateField(auto_now_add=True)
    actual_completion_date = models.DateField(blank=True, null=True)
    actual_project_costs = models.DecimalField(max_digits=10, decimal_places=2,
            blank=True, null=True)

Answer 1

You’re essentially dealing with apples and apples here. Django’s implementation of MTI (multi-table inheritance) uses an implicit OneToOneField.