[Answered ]-Prevent change of field if related objects exist?

by

2👍

✅

You can actually use model-level validation:

class Survey(models.Model):
    survey_type = models.CharField(max_length=1, choices=SURVEY_TYPES)

    def __init__(self, *args, **kwargs):
        super().__init__(self, *args, **kwargs)
        self._old_survey_type = self.survey_type

    def clean(self):
        if (self.survey_type != self._old_survey_type) \
                and survey_typeself.response_set.exists():
            raise ValidationError('Cannot modify the type of a started survey')

Be careful though, Model.clean is not automatically called when you save an object. It does when when a ModelForm gets validated (hence also in admin), but otherwise you have to check if it does or call it yourself.

👤Ivan

0👍

set survey and response field in Response model unique by
unique together like this:

class Response(models.Model):
    survey = models.ForeignKey(Survey)
    response = models.TextField()

    class Meta:
        unique_together = (("survey", "response"),)
👤Hasan Ramezani

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