Django `UniqueConstraint` exception handled the same as 'unique=True'

When UniqueConstraint of a model is violated, an exception is raised. How can I make it to behave the same as violation of a field with unique=True?

identifier = models.CharField("id", max_length=30, unique=True, blank=True, null=True, validators=[validate_id])

class Meta:
    constraints = [
        models.UniqueConstraint(
            Lower("identifier"),
            name="id_case_insensitive_constraint"
        )
    ]

Here I want a form's form_invalid called with the same field errors and all that, whether the input is exactly the same as another one or its only difference is case distinction.

The constraints are not translated into validators: the validation is done entirely at the database side, so Django can not know in advance that the item will be invalid.

You can make a validator, for example in the ModelForm to validate this yourself, with:

from django import forms
from django.core.exceptions import ValidationError

class MyModelForm(forms.ModelForm):
    
    def clean_identifier(self):
        data = self.cleaned_data['identifier']
        if MyModel.objecs.exclude(pk=self.instance.pk).filter(identifier__iexact=data).exists():
            raise ValidationError('The identifier already exists')
        return data
    
    class Meta:
        model = MyModel
        fields = ['identifier']