Unique constraints are not validated by clean

[tartieret]

Context

As mentioned in the documentation (https://django-safedelete.readthedocs.io/en/latest/models.html#fields-uniqueness), if we need to define a field uniqueness for non-deleted objects, we have to define a custom constraint such as:

class Product(SafeDeleteModel):

    name = models.CharField(
        max_length=100, verbose_name=_("name"), help_text=_("Name of the product")
    )

    class Meta:
        constraints = [
            models.UniqueConstraint(
                fields=["name"],
                condition=Q(deleted=None),
                name="product_unique_if_not_deleted",
            )
        ]

However, since we have to add a "condition" on the constraint, Product.has_unique_fields returns False and uniqueness validation is not performed when calling the model .clean method. This means that any model implementing this strategy has to implement custom validation for it

Root cause

The django model has_unique_fields and _perform_unique_checks are overwritten in models.SafeDeleteModel, but they exclude unique constraints with conditions, as shown below:

Solution

A potential solution is to modify the overwritten has_unique_fields and _perform_unique_checks. I am happy to submit a PR for these changes, but what do you think of this change @Gagaro @AndreasBackx @palkeo ?

[Gagaro]

We should (hopefully) have that fixed with Django 4.1 (cf django/django#14625).

With this change, we'll have to refactor a bit what we are doing in safedelete to make it all work.

[tartieret]

Looks like you are on top of it ! 😄
It makes sense to solve this in Django itself. Please let me know if you need help with the changes to django-safedelete, we use it at work and could allocate some time to it if needed