#34319: Model.validate_constraints check for ValidationError code
-------------------------------------+-------------------------------------
     Reporter:  Mateusz Kurowski     |                    Owner:  nobody
         Type:  Bug                  |                   Status:  new
    Component:  Database layer       |                  Version:  4.1
  (models, ORM)                      |
     Severity:  Normal               |               Resolution:
     Keywords:  Model,               |             Triage Stage:
  validate_constraints,              |  Unreviewed
  ValidationError, code, message     |
    Has patch:  0                    |      Needs documentation:  0
  Needs tests:  0                    |  Patch needs improvement:  0
Easy pickings:  0                    |                    UI/UX:  0
-------------------------------------+-------------------------------------

Comment (by Mateusz Kurowski):

 Maybe all unique constraints should allow raising validation error for
 specific field like ?


 {{{

 class ViolationFieldNameMixin:
     """
     Mixin for BaseConstraint subclasses that builds custom
     ValidationError message for the `violation_field_name`.
     By this way we can bind the error to the field that caused it.
     This is useful in ModelForms where we can display the error
     message next to the field and also avoid displaying unique
     constraint violation error messages more than once for  the same
 field.
     """

     def __init__(self, *args, **kwargs):
         self.violation_field_name = kwargs.pop("violation_field_name",
 None)
         super().__init__(*args, **kwargs)

     def validate(self, *args, **kwargs):
         try:
             value = super().validate(*args, **kwargs)
         except ValidationError as e:
             # Create a new ValidationError with the violation_field_name
 attribute as the key
             e = ValidationError({self.violation_field_name: e})
             # Set the error code to None
             # See https://code.djangoproject.com/ticket/34319#ticket
             e.code = "unique"
             raise e
         return value

     def deconstruct(self):
         path, args, kwargs = super().deconstruct()
         kwargs["violation_field_name"] = self.violation_field_name
         return path, args, kwargs

     def __eq__(self, other):
         return (
                 super().__eq__(other)
                 and self.violation_field_name == getattr(other,
 "violation_field_name", None)
         )


 class UniqueConstraint(ViolationFieldNameMixin, models.UniqueConstraint):
     ...

 }}}

-- 
Ticket URL: <https://code.djangoproject.com/ticket/34319#comment:1>
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