Adding attributes into Django Model's Meta class

Question

I'm writing a mixin which will allow my Models to be easily translated into a deep dict of values (kind of like .values(), but traversing relationships). The cleanest place to do the definitions of these seems to be in the models themselves, a la:

class Person(models.Model, DeepValues):
    name = models.CharField(blank=True, max_length=100)
    tribe = models.ForeignKey('Tribes')

    class Meta:
        schema = {
            'name' : str,
            'tribe' : {
                'name' : str
            }
        }

Person.objects.all().deep_values() => {
    'name' : 'Andrey Fedorov',
    'tribe' : {
        'name' : 'Mohicans'
    }
}

However, Django complains about my including this in class Meta with:

TypeError: 'class Meta' got invalid attribute(s): schema

(entire stack trace here)

Now, I suppose I could elaborately override this in my mixin, but is there a more elegant way of storing this information?

Carl Meyer · Accepted Answer · 2009-07-07 18:02:26Z

66

I don't know about elegant, but one pragmatic way is:

import django.db.models.options as options

options.DEFAULT_NAMES = options.DEFAULT_NAMES + ('schema',)

Obviously, this would break if Django ever added a 'schema' attribute of its own. But hey, it's a thought...you could always pick an attribute name which is less likely to clash.

edited Jul 7, 2009 at 18:02

Carl Meyer

127k21 gold badges111 silver badges117 bronze badges

answered Jul 6, 2009 at 18:50

Vinay Sajip

100k15 gold badges184 silver badges196 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Andrey Fedorov Over a year ago

For posterity's sake, that doesn't work, but this did: options.DEFAULT_NAMES = options.DEFAULT_NAMES + ('default_values',)

Vinay Sajip Over a year ago

Oh... it's presumably because my solution converts DEFAULT_NAMES to a list, whereas your refinement keeps it as a tuple.

PowerAktar Over a year ago

This works well for me options.DEFAULT_NAMES = (*options.DEFAULT_NAMES, 'my_custom_attr')

user1383029 · Accepted Answer · 2020-10-09 08:23:19Z

5

Not a direct answer, but I did not like the idea of adding it in every model where I need it to the options, so I did:

class MyModel(models.Model):
    
    class Meta:
        ordering = ["myfield"]

    class MyPrefixMeta:
        my_value = "Abc"

You could even put this to a abstract model and validate the set class properties in __init__ function or do things like adding a _myprefix_meta property to the model. So you had your own meta class.

answered Oct 9, 2020 at 8:23

user1383029

2,1552 gold badges24 silver badges43 bronze badges

Comments

Nihal Sharma · Accepted Answer · 2021-02-11 11:59:57Z

3

This works for me for setting extra fields in meta for a Django model.

class Vendor(CustomModel):

    def __init__(self, *args, **kwargs):
        cls = self.__class__
        meta = getattr(cls, '_meta', None)
        setattr(meta, 'exclude_logging', ["otp", "is_otp_verified"])
        super().__init__(*args, **kwargs)

This exclude_logging field can be accessed as below.

class CustomModel(models.Model):

    objects = UpdateManager()

    class Meta:
        abstract = True

    def save(self, *args, **kwargs):
        print(self._meta.exclude_logging)

I hope this solves the problem.

answered Feb 11, 2021 at 11:59

Nihal Sharma

2,44712 gold badges44 silver badges58 bronze badges

1 Comment

MatsLindh Over a year ago

The detail about _meta being present saved me - any fields I added using the above method didn't materialize when accessing model.Meta directly, but looking under _meta (the actual instance) solved it! Thank you!

Andreas · Accepted Answer · 2024-09-25 11:31:04Z

0

To add to the above I have found another way to add custom attributes to a meta-class by simply prefixing the attribute with an underscore (_). So the above example would work as follows:

class Person(models.Model, DeepValues):
    name = models.CharField(blank=True, max_length=100)
    tribe = models.ForeignKey('Tribes')

    class Meta:
        _schema = {
            'name' : str,
            'tribe' : {
                'name' : str
            }
        }

edited Sep 25, 2024 at 11:31

answered Sep 25, 2024 at 11:01

Andreas

1,18219 silver badges35 bronze badges

Collectives™ on Stack Overflow

Adding attributes into Django Model's Meta class

4 Answers 4

3 Comments

Comments

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related