Help a Python newbie with a Django model inheritance problem

Question

I'm working on my first real Django project after years of PHP programming, and I am running into a problem with my models. First, I noticed that I was copying and pasting code between the models, and being a diligent OO programmer I decided to make a parent class that the other models could inherit from:

class Common(model.Model):
    name = models.CharField(max_length=255)
    date_created  = models.DateTimeField(auto_now_add=True)
    date_modified = models.DateTimeField(auto_now=True)

    def __unicode__(self):
        return self.name

    class Meta:
        abstract=True

So far so good. Now all my other models extend "Common" and have names and dates like I want. However, I have a class for "Categories" were the name has to be unique. I assume there should be a relatively simple way for me to access the name attribute from Common and make it unique. However, the different methods I have tried to use have all failed. For example:

class Category(Common):
    def __init__(self, *args, **kwargs):
        self.name.unique=True

Causes the Django admin page to spit up the error "Caught an exception while rendering: 'Category' object has no attribute 'name'

Can someone point me in the right direction?

Community · Accepted Answer · 2017-05-23 12:01:15Z

2

No, Django doesn't allow that.

See the docs: http://docs.djangoproject.com/en/1.1/topics/db/models/#field-name-hiding-is-not-permitted

Also answered in other questions like: In Django - Model Inheritance - Does it allow you to override a parent model's attribute?

edited May 23, 2017 at 12:01

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answered May 26, 2010 at 16:40

gomad

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2 Comments

Joshmaker Over a year ago

I'm a little shocked to see that in the docs... that seems like a pretty big omission!

gomad Over a year ago

Well, model inheritance was missing entirely from Django for quite some time, so I think this is a big improvement. I'm not entirely sure, but I think you might be able to implement your unique=true in a custom manager. Or, you might be able to use multiple inheritance and have the UNIQUE_NAME as a mixin.

Mark Lavin · Accepted Answer · 2010-05-26 15:38:36Z

1

You have a small mistake in your Common class

class Common(model.Model):
    self.name = models.CharField(max_length=255)

should be

class Common(model.Model):
    name = models.CharField(max_length=255)

answered May 26, 2010 at 15:38

Mark Lavin

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2 Comments

Daniel Roseman Over a year ago

think that must be a copy-and-paste issue, since it's not valid Python - self isn't defined at that point.

Joshmaker Over a year ago

Sorry about the confusion over the typo. Since I am new to Python I've been experimenting with lots of odd code just to see what happens, and that was one of my experiments which I meant to clean up before pasting into Stackoverflow. Unfortunately, my code doesn't work even with the typo removed

Tomasz Zieliński · Accepted Answer · 2010-05-26 23:11:05Z

1

Note that UNIQUE constraint in fact has nothing to do with Django, so you're free to add it in your database table. You can also use post-syncdb hook for that purpose.

answered May 26, 2010 at 23:11

Tomasz Zieliński

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Comments

Ignacio Vazquez-Abrams · Accepted Answer · 2010-05-26 16:45:15Z

0

Try using Meta.unique_together to force it into its own unique index. Failing that, it's probably easiest to create two separate abstract classes, one with the field unique and one not.

answered May 26, 2010 at 16:45

Ignacio Vazquez-Abrams

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