Model field based on other fields?

Question

Can I have a model field be based on other fields? For example:

class Foo(models.Model):
    x = models.PositiveSmallIntegerField()
    y = models.PositiveSmallIntegerField()
    z = models.PositiveSmallIntegerField()

    score = models.PositiveSmallIntegerField(default=x+y+z)

score 22 · Accepted Answer · answered Mar 03 '14 at 21:17

22

Yes, the best way to handle this would be to override the save method of the model

class Foo(models.Model):
    x = models.PositiveSmallIntegerField()
    y = models.PositiveSmallIntegerField()
    z = models.PositiveSmallIntegerField()

    score = models.PositiveSmallIntegerField()

    def save(self, *args, **kwargs):
        self.score = self.x + self.y + self.z
        super(Foo, self).save(*args, **kwargs) # Call the "real" save() method.

Make sure you take care of the necessary validations.

More on this here: official documentation

answered Mar 03 '14 at 21:17

karthikr

97,368
26
197
188

Thank you, this worked perfectly for me... Now I am trying to interpret `models.BooleanField` as 0 or 1 integers to add up and score. – broinjc Mar 04 '14 at 00:18
Just do `sum([...])` Example: `sum([True, False, True, True])` = 3 – karthikr Mar 04 '14 at 01:40

score 10 · Answer 2 · answered Mar 15 '19 at 09:23

10

How about this?

class Foo(models.Model):
     x = models.PositiveSmallIntegerField()
     y = models.PositiveSmallIntegerField()
     z = models.PositiveSmallIntegerField()

     @property
     def score(self):
         return self.x + self.y + self.z

Official docs on Model Methods here

answered Mar 15 '19 at 09:23

Daryl Lukas

155
2
10

Great answer, especially when you can't rely on the .save() method being called in e.g., a batch update – Liz Jul 22 '19 at 03:24
Any way to use an object like this score in a list_filter? – Vaidøtas I. Jun 25 '23 at 18:40

Model field based on other fields?

2 Answers2

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