Accessing model instance from validator

Question

How would I access the instance of the model that is being validated from within the validator for a specific field?

models.py

def question_instances(value):  #validator     
   # not sure how to get model instance within this function

   industry = model_instance.industry
   questions = Question.objects.filter(industry=industry)
   if questions.count() > 3:
      raise ValidationError('Too many questions for this industry')

class ExampleQuestion(models.Model):
    industry = models.ForeignKey(Industry, on_delete=models.CASCADE)    
    question = models.CharField(max_length=200, validators=[question_instances])

    def __str__(self):
        return self.industry.industryname

Why do you think you need this? The `value` parameter contains the value for industry. — Daniel Roseman, Mar 09 '19 at 20:34
Hi Daniel, Good to talk to you again. After I posted my question, I realized this. I moved the validator to the industry line in the model. However, within the validator, I now need to get the model instance so that I can check to see if I'm creating a new model or editing an existing one. That will dictate if I use > 3 or > 4 as the condition. Thanks Daniel — Jason Howard, Mar 09 '19 at 20:41

score 12 · Accepted Answer · answered Mar 09 '19 at 21:19

You can't. If you need this, don't use a validator; use a clean function instead.

class ExampleQuestion(models.Model):
    industry = models.ForeignKey(Industry, on_delete=models.CASCADE)    
    question = models.CharField(max_length=200)

    def clean(self):
         industry = self.industry
         questions = Question.objects.filter(industry=industry).exclude(pk=self.pk)
         if questions.count() > 3:
             raise ValidationError('Too many questions for this industry')

This will not work in DRF, any common solution? – Krishnadas PC Jun 02 '22 at 10:01 — Krishnadas PC, Jun 02 '22 at 10:01

Accessing model instance from validator

1 Answers1