How to add index to my slug if it already exists in database?

Question

When i create new post i need to do next:

1. Generate slug from self.title with slugify
2. Check if this slug does not exists we save post with self.slug
3. If this slug already exists we save post with self.slug + '-' + count index

I found worked solution but i'm new in django so i want to ask you is this optimal solution?

#models.py

from django.db import models
from django.shortcuts import reverse
from django.utils.text import slugify
from django.db.models.signals import post_save
from django.dispatch import receiver

class Post(models.Model):
    title = models.CharField(max_length=150, db_index=True)
    slug = models.SlugField(max_length=150, blank=True, unique=True)

    def get_absolute_url(self):
        return reverse('post_detail_url', kwargs={'slug': self.slug})

@receiver(post_save, sender=Post)
def set_slug(sender, instance, *args, **kwargs):
    if not instance.slug:
        instance.slug = slugify(instance.title)
        while Post.objects.filter(slug__startswith=instance.slug).exists():
            instance.slug += '-' + str(Post.objects.filter(slug__startswith=instance.slug).count())
        instance.save()

No more crashes but i need to ask is my solution optimal? Post edited — Алексей Малиновский, May 25 '19 at 11:59
It is not bad. But you shouldn't override save unless you really need to do so. I think a [pre-save signal](https://docs.djangoproject.com/en/2.2/ref/signals/#pre-save) is most suited for what you are trying to do. I can compose a proper answer showing you how to use it if you want me to. — Stargazer, May 25 '19 at 12:10

Stargazer · Accepted Answer · 2019-05-25T12:49:17.380

0

A pre-save signal is the best way to deal with this. Everytime a instance is about to get save, the signal will be triggered and run some logic. In this case, it will populate the slug field before saving.

from django.db.models.signals import pre_save
from django.dispatch import receiver

# you other stuff goes here

@receiver(pre_save, sender=MyModel)
def set_slug(sender, instance, *args, **kwargs):
    instance.slug = slugify(instance.title)

And that is it!

If your signals is not connected around apps, you can place it on your models.py. But if you are using it to connect different apps, or a common signal to multiple apps, you can should have a separated file to place.

Just a note: see that sender=MyModel piece? That is tying the signal to a specific model. If you have a lot of models that would use slugs, you can just remove it to make the pre save hook available to multiple models.

edited May 25 '19 at 12:49

answered May 25 '19 at 12:28

Stargazer

1,442
12
19

Where should i put this code? Can you post full code for my case? I don't actually understand how to implement this. – Алексей Малиновский May 25 '19 at 12:40
I wrote there. If you don't have many signals, or the signals are to be used on the on single app, just put them in your `models.py` – Stargazer May 25 '19 at 12:42
Undefined variable @receiver – Алексей Малиновский May 25 '19 at 12:48
Oh sorry, forgot the receiver import. Fixed. – Stargazer May 25 '19 at 12:49
But i need to save it 2 times: first one to have self.id and second is to save self.slug – Алексей Малиновский May 25 '19 at 12:54
Well, I didn't quite understand what you were doing if the id, but you shouldn't use ids on your slugs, otherwise you are defeating the purpose of the slug. – Stargazer May 25 '19 at 12:57
Oh, now I get what your mean. You just have to to check if the slugs already exists before calling slugify. You can do something like: `if MyClass.objects.filter(slug=instance.title).exists(): instance.slug = slugify(f"{instance.title}-{random.randint(1,100)}` – Stargazer May 25 '19 at 13:01
I don't really want to use random numbers. How can i get self.id before it will be added in database? – Алексей Малиновский May 25 '19 at 13:05
You can't What you can do is change the `pre_save` signal for a `post_save` signal, that will behave almost the same way, but it will be called after it's saved, so you will be able to call `instance.id`. But be aware that you will need to add a `created` argument in the function. If created is `true`, it means that instance was just created and you should add the slug. Otherwise, it was just edited, so it doesn't need a slug. [Check here the docs for pre_save](https://docs.djangoproject.com/en/2.2/ref/signals/#pre-save) – Stargazer May 25 '19 at 13:09
But again, you shouldn't use ids on your slugs. – Stargazer May 25 '19 at 13:09
you could use the count as the index: `instance.slug= slufify(f"{instance.title}-{Post.objects.filter(slug__startswith=instance.title).count() + 1}")` – Stargazer May 25 '19 at 13:19
Great idea with count! I have edit my code as you recommended but it creates a post with empty slug. I edited my first post, what sould i fix? – Алексей Малиновский May 25 '19 at 14:10
Ok, now ot works but we have another issue. If i make post with slug = 'foo-3' and then will make 3 posts with slug = 'foo' it will create: foo-1, foo-2, and then we will have database error cause our 'foo-3' already exists. – Алексей Малиновский May 25 '19 at 14:34
Ok i fixed. It will now add 'foo-1', 'foo-2', 'foo-3-1', 'foo-4' etc – Алексей Малиновский May 25 '19 at 15:04

How to add index to my slug if it already exists in database?

1 Answers1