Django, assigning a composite value to one field depending upon values entered in other fields in same model?

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I am new to django. What I am currently trying to do is set a value which is a primary key and non-editable automatically generated depending upon the values entered in the same model to some other fields. Here is an example:

   class Student(models.Model):
      student_id = models.CharField(max_length=100, primary_key=true)
      name  = models.CharField(max_length=100)
      class  = models.CharField(max_length=200)
      roll_no  = models.CharField(max_length=500)

So, what I am trying to achieve is if someone enters following information :

name = Haris
class = 8th
roll_no = 104011

The automatically generated primary key that would be non-editable for field "student_id" would be:

student_id = Haris_8th_104011

Does anyone have an idea how to achieve this? Hope my example made the query clear though.

django-forms django-views django-models django python
1 Answers

You can do this way overriding save method. Note that class variable clashesh with original builtin class name please migrate once as i changed the variable name

class Student(models.Model):
    student_id = models.CharField(max_length=100, primary_key=True, editable=False)
    name = models.CharField(max_length=100)

    classes = models.CharField(max_length=200)

    roll_no = models.CharField(max_length=500)

    def save(self, *args, **kwargs):
        self.student_id = f'{self.name}_{self.classes}_{self.roll_no}'
        super(Student,self).save(*args, **kwargs)
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