Django: How to set a integer field max value based on Foreign Key atribute?

Question

I have the following model:

class Atividades_cumpridas(models.Model):
    id_atividade = models.ForeignKey(Atividade, on_delete=models.CASCADE)
    id_jogador = models.ForeignKey(Jogador, on_delete=models.CASCADE)
    pontos_xp_ganhos = models.IntegerField()

    def __str__(self):
        str = self.id_atividade.nome_atividade + ' - ' + self.id_jogador.nome_jogador
        return str

and i want to set the pntos_xp_ganhos max value based on Atividade.pontos_XP_maximo. How can I do that and show the max value on the admin editing page?

Nicolò Gasparini · Accepted Answer · 2018-10-05 22:21:03Z

2

There are two ways you can do it,

Using custom validators
Using builtin validators

custom validators:

from django.core.exceptions import ValidationError

def validate_range(value):
    if value > Atividade.pontos_XP_maximo:
        raise ValidationError('Max value should be %s' % Atividade.pontos_XP_maximo
        )

class Atividades_cumpridas(models.Model):
        ...
        ...
        pontos_xp_ganhos = models.IntegerField(validators=[validate_range])

Using builtin validators:

MIN = 0
MAX = Atividade.pontos_XP_maximo
from django.core.validators import MinValueValidator, MaxValueValidator

class Atividades_cumpridas(models.Model):
    ...
    ...
    pontos_xp_ganhos = models.IntegerField(validators=[MinValueValidator(MIN), MaxValueValidator(MAX)]

edited Oct 5, 2018 at 22:21

Nicolò Gasparini

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answered Apr 24, 2018 at 14:30

Nishant Nawarkhede

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6 Comments

Ronaldo Silveira Over a year ago

but for each Atividade i have a different pontos_XP_maximo

Nishant Nawarkhede Over a year ago

@RonaldoSilveira can please explain with example ?

Ronaldo Silveira Over a year ago

For example: If i have an Atividade with id = 1, i would have, let's say, pontos_XP_maximo = 30. For the Atividade with id = 2, it would be 50.

Nishant Nawarkhede Over a year ago

@RonaldoSilveira is Atividade and pontos_XP_maximo are predefined >

Ronaldo Silveira Over a year ago

No, Atividade is a model and pontos_XP_maximo is a field. So they are in te database and may be altered.

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AlirezaAsadi · Accepted Answer · 2022-04-13 09:50:04Z

0

You can override clean() method in your model and do the validation there. As Django docs states:

This method should be used to provide custom model validation, and to modify attributes on your model if desired. For instance, you could use it to automatically provide a value for a field, or to do validation that requires access to more than a single field.

And in your case, you want to do a validation that requires access to more than a single field, which makes clean a proper method to do what you desire.

Note, however, that like Model.full_clean(), a model’s clean() method is not invoked when you call your model’s save() method.
You can see how to fix this here: Django doesn't call model clean method

answered Apr 13, 2022 at 9:50

AlirezaAsadi

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