python 40 lines · 7 steps

Auto-generating unique slugs in Django

A Django model that derives a unique slug from its title and keeps it in sync whenever the title changes.

Explained by highlit

Django Intermediate slugs orm model-methods save-override uniqueness

1from django.db import models
2from django.utils.text import slugify
3 
4 
5class Article(models.Model):
  title = models.CharField(max_length=200)
  slug = models.SlugField(max_length=220, unique=True, editable=False)
  body = models.TextField()
  published_at = models.DateTimeField(null=True, blank=True)
10 
  class Meta:
      ordering = ["-published_at"]
13 
  def __str__(self):
      return self.title
16 
  def save(self, *args, **kwargs):
      if not self.slug or self._title_changed():
          self.slug = self._unique_slug()
      super().save(*args, **kwargs)
21 
  def _title_changed(self):
      if not self.pk:
          return True
      old_title = Article.objects.filter(pk=self.pk).values_list("title", flat=True).first()
      return old_title != self.title
27 
  def _unique_slug(self):
      base = slugify(self.title)[:200] or "article"
      slug = base
      siblings = Article.objects.exclude(pk=self.pk)
      suffix = 2
      while siblings.filter(slug=slug).exists():
          slug = f"{base}-{suffix}"
          suffix += 1
      return slug
37 
  def get_absolute_url(self):
      from django.urls import reverse
      return reverse("article_detail", kwargs={"slug": self.slug})

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STEP 01

Walkthrough

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Three takeaways

1Overriding save lets a model compute derived fields before every write.
2Comparing against the stored row detects field changes without extra state.
3Appending an incrementing suffix guarantees uniqueness under a unique constraint.

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