Django model instance custom method

Question

I'm trying to integrate a custom method on a Django model

class Post(models.Model):
    author = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, blank=True)
    title = models.CharField(max_length=200)
    text = MarkdownField()
    slug = models.SlugField(unique=True, blank=True)
    created = models.DateTimeField(auto_now_add=True)
    published_date = models.DateTimeField(blank=True, null=True)

    def generate_unique_slug(self):
        slug = self._meta.get_field('slug')
        max_length = slug.max_length
        slug = orig = slugify(self.title)[:max_length]

        for x in itertools.count(1):
            if not Post.objects.filter(slug=slug).exists():
                break

            # Truncate the original slug dynamically. Minus 1 for the hyphen.
            slug = "%s-%d" % (orig[:max_length - len(str(x)) - 1], x)

    def publish(self):
        self.published_date = timezone.now()
        self.generate_unique_slug()
        self.save()

When called from "publish", "generate_unique_slug" doesn't work. For example, I'll do this from terminal

>>> p = Post(title="Title Example", text="Text example")
>>> p.publish()
>>> p.title
'Title Example'
>>> p.published_date
datetime.datetime(2016, 6, 18, 14, 45, 12, 710452, tzinfo=<UTC>)
>>> p.slug
u''

I've also tried this

>>> p.generate_unique_slug()
>>> p.slug
u''

What am I doing wrong?

Moses Koledoye · Accepted Answer · 2016-06-18 14:53:28Z

1

You're not updating the slug of your model. Add self.slug = slug at the end of generate_unique_slug:

def generate_unique_slug(self):
    # your code
    self.slug = slug

answered Jun 18, 2016 at 14:53

Moses Koledoye

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4 Comments

Stefano De Rosso Over a year ago

That's it, thanks! Anyway, when I create the Post from the admin panel, the slug isn't created: any thoughts on how I might get that?

Martin Hallén Over a year ago

The slug is generated only when you run the publish function. Is this where your problem is? If so, you probably want to override the save method.

Moses Koledoye Over a year ago

Because the method will not be called when creating a new Post. You can modify the save method of your model to always call generate_unique_slug. See this

Stefano De Rosso Over a year ago

Thank you. I made it by overriding the save method, and putting "super(Post, self).save()" at the end.

DeepSpace · Accepted Answer · 2016-06-18 14:55:51Z

0

generate_unique_slug neither change any instance attribute nor return anything.

You should change slug in slug = "%s-%d" % (orig[:max_length - len(str(x)) - 1], x) to self.slug = ....

answered Jun 18, 2016 at 14:55

DeepSpace

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Comments

Martin Hallén · Accepted Answer · 2016-06-18 15:30:56Z

This answer does not fix your code, but I think it is a good option as it covers multiple cases.

There is a library called uuslug designed to do exactly this. It might be worth checking out.

A example from the repository:

from django.db import models
from uuslug import uuslug

# Override your object's save method with something like this (models.py)
class CoolSlug(models.Model):
    name = models.CharField(max_length=100)
    slug = models.CharField(max_length=200)

    def __unicode__(self):
        return self.name

    def save(self, *args, **kwargs):
        self.slug = uuslug(self.name, instance=self)
        super(CoolSlug, self).save(*args, **kwargs)

name = "john"
c = CoolSlug.objects.create(name=name)
c.save()
print(c.slug) # => "john"

c1 = CoolSlug.objects.create(name=name)
c1.save()
print(c1.slug) # => "john-1"

I also believe you can change slug = models.CharField(max_length=200) to slug = models.SlugField(max_length=200), and it would still work properly.

Edit after comment:

Instead of overriding save, you could do the following:

from uuslug import slugify

class Post(models.Model):
    author = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, blank=True)
    title = models.CharField(max_length=200)
    text = MarkdownField()
    slug = models.SlugField(unique=True, blank=True)
    created = models.DateTimeField(auto_now_add=True)
    published_date = models.DateTimeField(blank=True, null=True)


    def publish(self):
        self.published_date = timezone.now()
        self.slug = slugify(self.title, max_length=self._meta.get_field('slug'))
        self.save()

Does this fix the problem?

Thanks for the library, anyway I think you misread the line, as the slug line is "slug = models.SlugField(unique=True, blank=True)" :)

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