Primary Keys, IDs, Slugs, UUIDs of model object in Django

Primary Keys vs. IDs

Django generic.DetailView treats them interchangeably. There is a subtle difference.

id is a model field automatically set by Django internally to auto-increment, such as 1, 2, 3, and so on. This is also treated as the primary key pk of a model.

However it’s possible to manually change what the primary key is for a model. It doesn’t have to be id.

By contrast the primary key pk refers to the primary key field of a model, so it’s safe using pk even we changed the id of our model.

Slugs vs. UUIDs

slug is a newspaper term for a short label for something, that is often used in URLs. There is a SlugField model field. The main challenge with slugs is handling duplicates.

Django supports UUID with a UUIDField model field. In production, we usually update the model’s default id with UUID field and use it in the URL path.

Update id with UUIDField in model

import uuid
from django.db import models
from django.urls import reverse

class Book(models.Model):
    id = models.UUIDField(
        primary_key=True,
        default=uuid.uuid4,
        editable=False
    )
    title = models.CharField(max_length=200)
    author = models.CharField(max_length=200)
    price = models.DecimalField(max_digits=6, decimal_places=2)

    def __str__(self):
        return self.title

    # canonical URL for the model
    def get_absolute_url(self):
        return reverse('book_detail', args=[str(self.pk)])

replace int with uuid in urls

from django.urls import path

from .views import BookListView, BookDetailView

urlpatterns = [
    path('', BookListView.as_view(), name="book_list"),
    path("<uuid:pk>/", BookDetailView.as_view(), name="book_detail")
]

migration

The main challenge with migration is handling the existing records, the existing id value is not compatible with the update UUID field.

The most destructive approach is to simply delete old migrations and records and then start over.