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):
6 title = models.CharField(max_length=200)
7 slug = models.SlugField(max_length=220, unique=True, editable=False)
8 body = models.TextField()
9 published_at = models.DateTimeField(null=True, blank=True)
10 
11 class Meta:
12 ordering = ["-published_at"]
13 
14 def __str__(self):
15 return self.title
16 
17 def save(self, *args, **kwargs):
18 if not self.slug or self._title_changed():
19 self.slug = self._unique_slug()
20 super().save(*args, **kwargs)
21 
22 def _title_changed(self):
23 if not self.pk:
24 return True
25 old_title = Article.objects.filter(pk=self.pk).values_list("title", flat=True).first()
26 return old_title != self.title
27 
28 def _unique_slug(self):
29 base = slugify(self.title)[:200] or "article"
30 slug = base
31 siblings = Article.objects.exclude(pk=self.pk)
32 suffix = 2
33 while siblings.filter(slug=slug).exists():
34 slug = f"{base}-{suffix}"
35 suffix += 1
36 return slug
37 
38 def get_absolute_url(self):
39 from django.urls import reverse
40 return reverse("article_detail", kwargs={"slug": self.slug})
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1Overriding save lets a model compute derived fields before every write.
  2. 2Comparing against the stored row detects field changes without extra state.
  3. 3Appending an incrementing suffix guarantees uniqueness under a unique constraint.

Related explainers

python 
from django.db.models import Prefetch, Count
from django.views.generic import ListView
 
from .models import Article, Comment

Building an efficient article list in Django

orm query-optimization prefetching
Intermediate 6 steps
python 
from functools import lru_cache
import math
 
 

Memoizing number theory with lru_cache

memoization number-theory caching
Intermediate 8 steps
python 
import re
from collections import defaultdict
from pathlib import Path
 

Summarizing log files by date in Python

regex parsing aggregation
Intermediate 7 steps
python 
import threading
import logging
 
logger = logging.getLogger(__name__)

A self-rescheduling periodic task in Python

threading scheduling concurrency
Intermediate 6 steps
python 
from collections import ChainMap
from functools import reduce
from typing import Any, Iterable, Mapping
 

Five ways to merge dicts in Python

dictionaries merging recursion
Intermediate 8 steps
python 
from fastapi import Depends, FastAPI, HTTPException
from sqlalchemy import create_engine
from sqlalchemy.orm import Session, sessionmaker
 

Wiring SQLAlchemy sessions into FastAPI

dependency-injection orm sessions
Intermediate 7 steps

Share this explainer

Here's the card — post it anywhere.

Auto-generating unique slugs in Django — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code