How to define two Django fields unique in certain conditions

Question

I want to make Django Model fields unique with two fields(values) in some conditions.

there's two fields: 'team', 'type'. And I want to make team manager unique

For Example:

team=1, type='manager'
team=1, type='manager'

-> Not available

team=1, type='manager'
team=1, type='member'
team=1, type='member'
team=2, type='manager'

-> Available

I think unique_together('team', 'type') won't work properly with this situation.

How can I make this with Django Model?

Here's my model below:

class myModel(models.Model):
    team = models.ForeignKey('Team', on_delete=models.CASCADE)
    type = models.CharField(max_length=10, default='member')
    class Meta:
        db_table = 'my_models'

welcome, have you added `unique_together('team', 'type')` in Meta ? — Devang Hingu, Jul 12 '20 at 16:38
you need to define another table(like **TypeOfUser**) which ref needs to give with ` type ` so only those ref. accepted which exist on **TypeOfUser** so that on will work with `unique_together('team', 'type')` — Devang Hingu, Jul 12 '20 at 16:42
I want to make unique only if type=='manager'. Does `unique_together('team', 'type')` works? — GartenChoi, Jul 12 '20 at 16:44

score 1 · Answer 1 · answered Jul 12 '20 at 16:55

I think, You need to use UniqueConstraint for your application which work perfect in kind of situation.

class myModel(models.Model):
    team = models.ForeignKey('Team', on_delete=models.CASCADE)
    type = models.CharField(max_length=10, default='member')
    class Meta:
        db_table = 'my_models'
        constraints = [
             models.UniqueConstraint(fields=['team', 'type'], name='unique_team')
        ]

you can also refer this link for more understanding. and let me know if following solution will work.

I want to make unique only if type=='manager'. type=="member" can be duplicate. I think UniqueConstraint is not appreciate for my app :-( — GartenChoi, Jul 17 '20 at 09:49

score 1 · Answer 2 · answered Oct 26 '21 at 18:40

Given that there is a deprecation warning in the documentation (based on 3.2 docs) for unique_together, I think it's worth showing that this can be done using UniqueConstraint. I believe that the key missing ingredient from the previous answer is the use of UniqueConstraint.condition, like so:

from django.db import models
from django.db.models import Q, UniqueConstraint

class myModel(models.Model):
    team = models.ForeignKey('Team', on_delete=models.CASCADE)
    type = models.CharField(max_length=10, default='member')
    class Meta:
        db_table = 'my_models'
        constraints = [
            UniqueConstraint(
                fields=['team', 'type'],
                name='unique_team',
                condition=Q(type='manager')
            )
        ]

How to define two Django fields unique in certain conditions

2 Answers2