Creating models.UniqueConstraint in django, but the constraint is not applying - django

Question

My table is defined as below.
class Role(models.Model):
user = models.ForeignKey(
settings.AUTH_USER_MODEL,
to_field="email",
db_column="user",
on_delete=models.CASCADE
)
vertical = models.ForeignKey(
Verticals,
to_field="name",
db_column="vertical",
on_delete=models.CASCADE
)
product_domain = models.ForeignKey(
ProductDomains,
to_field="name",
db_column="product_domain",
null=True,
on_delete=models.CASCADE
)
class Meta:
constraints = [
models.UniqueConstraint(fields=[
'user',
'vertical',
'product_domain'
],
name='unique-permissions-per-user')
]
Here are the migrations that are generated
migrations.CreateModel(
name='Role',
fields=[
('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
('product_domain', models.ForeignKey(db_column='product_domain', null=True, on_delete=django.db.models.deletion.CASCADE, to='verticals.ProductDomains', to_field='name')),
('user', models.ForeignKey(db_column='user', on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL, to_field='email')),
('vertical', models.ForeignKey(db_column='vertical', on_delete=django.db.models.deletion.CASCADE, to='verticals.Verticals', to_field='name')),
],
),
migrations.AddConstraint(
model_name='role',
constraint=models.UniqueConstraint(fields=('user', 'vertical', 'product_domain'), name='unique-permissions-per-user'),
),
Serializers for the Role model is
class RoleSerializer(serializers.ModelSerializer):
class Meta:
model = Role
fields = '__all__'
Here is the interactive console for the same
Link to console image (Unable to add due to less reputation )
Here the UniqueConstraint is not working, why?
I use models.UniqueConstraint in the same project many times but it doesn't work in this case.
My configuration is
Django - 3.0.4
Django Rest Framework - 3.11.0
Database - MySql
Please help and ask if any information is missing out.

Answer 1

Your logs don't show any attempt to insert the same record into the DB twice, just validation.
It appears Django Rest Framework does not import constraints from UniqueConstraint, and only has code to validate with the old Meta.unique_together constraint definition.
There is a tracking issue, ModelSerializer not generating validators for constraints, on the DRF GitHub where you can follow the latest updates on adding support for UniqueConstraint validation.