(Photo by Lisa Nouwen)

When migrating from Plone to Django, I had problems with editing weblog entries with a dot in the url. Apparently Django doesn't allow dots in a SlugField. Here's how I solved it.

First a bit of background information. My previous site was in Plone and I had a number of weblog entries with a dot in the URL. I did not want to change those URLs but I also wanted to be able to edit the weblog entries.

The biggest problem I had, was getting the SlugField being validated if there was a dot in it. There's an old ticket (#5368) where this is discussed, but it has been closed as “wontfix.” The last comment pointed me in the right direction:

Slug fields are for a particular style of string. Underneath, though, they are just character fields with a validator. So if you want different validation requirements, just use a CharField and your own validator.

However, instead of using a CharField, I chose to create my own SlugField (MySlugField). This subclasses the Django SlugField but has a modified validator. In other words, my admin.py looks very similar to this:

import re
from django.contrib import admin
from django.core.validators import RegexValidator
from django.forms.fields import SlugField
from django.forms.models import ModelForm

from blog.models import BlogEntry


slug_re = re.compile(r'^[-\w.]+$')
validate_slug = RegexValidator(slug_re,
    u"Enter a valid 'slug' consisting of letters, numbers, underscores, "
    u"dots or hyphens.", 'invalid')


class MySlugField(SlugField):
    """A custom field where dots *are* allowed in the slug.
    This is needed for backwards compatibility with my Plone weblog items.
    """
    default_error_messages = {
        'invalid': u"Enter a valid 'slug' consisting of letters, numbers, "
                   u"underscores, dots or hyphens.",
    }
    default_validators = [validate_slug]


class BlogEntryForm(ModelForm):
    slug = MySlugField()

    class Meta:
        model = BlogEntry


class BlogEntryAdmin(admin.ModelAdmin):
    form = BlogEntryForm
    prepopulated_fields = {'slug': ['title']}

admin.site.register(BlogEntry, BlogEntryAdmin)

Now SlugFields with dots can just be saved. Making sure they can also be retrieved is easy. All you need to do is change (?P<slug>[-\w]+) in your URL pattern with (?P<slug>[-\w.]+).

(Note that by default dots are still filtered out by the script that prepopulates the SlugField. That's okay for me: I only did this for the old entries and can still insert the dot manually if I really want to.)