[FIXED] Check Constraint in Django

Issue

I want to include a check constraint for my model in my members app where the sex field should be male, female or null. Here is my code:

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

# Create your models here.
class Member(models.Model):
    firstname = models.CharField(max_length=255)
    lastname = models.CharField(max_length=255)
    telephonenum = models.IntegerField(null=True)
    sex = models.CharField(max_length=10, null=True)
    CheckConstraint(check=Q((sex == "Female") | (sex == "Male")), name="check_sex")

This code is not working I can still make sex field something different than Female or Male.

I've tried this code but it didn't work either:

from django.db import models

# Create your models here.
human_sex = (
    ("1", "Woman"),
    ("2", "Man"),
)

class Member(models.Model):

    firstname = models.CharField(max_length=255)
    lastname = models.CharField(max_length=255)
    telephonenum = models.IntegerField(null=True)
    sex = models.CharField(max_length=10, choices=human_sex, null=True)

Solution

You list the constraint in a list named constraints in the Meta of the model. You also used the Q object wrong, it should be used as a parameter name, like:

class Member(models.Model):
    firstname = models.CharField(max_length=255)
    lastname = models.CharField(max_length=255)
    telephonenum = models.IntegerField(null=True)
    sex = models.CharField(max_length=10, null=True)

    class Meta:
        constraints = [
            CheckConstraint(
                check=Q(sex='Female') | Q(sex='Male'), name='check_sex'
            )
        ]

Django by default does not enforce the choices at the database level, so only ModelForms and serializer will check this. Without the aim to do a lot of self-promotion, I made a small package that can enforce fields with choices at the database level named django-enforced-choices ^[GitHub]. After installing the package, you can add a mixin to your model with:

from django.db import models
from django_enforced_choices.models import ChoicesConstraintModelMixin

# Create your models here.
human_sex = (
    ('1', 'Woman'),
    ('2', 'Man'),
)


class Member(ChoicesConstraintModelMixin, models.Model):

    firstname = models.CharField(max_length=255)
    lastname = models.CharField(max_length=255)
    telephonenum = models.IntegerField(null=True)
    sex = models.CharField(max_length=10, choices=human_sex, null=True)

This will then automatically add the constraint we added explicitly in the first code fragment.

Answered By - willeM_ Van Onsem