Django Вычисление даты

Модель:

    class JobCycle(models.Model):   

          dateReceived = models.DateField(blank=True, null=True)
          dueDate = models.DateField(blank=True, null=True)
          dateOut = models.DateField(blank=True, null=True)
          fee = models.IntegerField(blank=True, null=True)
 

         def __str__(self):
            return "Job Cycle" + str(self.id)

         def save(self, *args, **kwargs):
            if self.dateReceived and self.dueDate:
               if self.dateReceived > self.dueDate:
                raise ValidationError(
                    'Due date will never be greater than the received date')
            super(JobCycle, self).save(*args, **kwargs)

Я хочу сделать расчет, чтобы срок исполнения никогда не превышал дату получения. Я хочу сделать это в модели

Вы можете переопределить метод сохранения модели save():

Перед или после def __str__ (на том же уровне) добавьте:

def save(self, *args, **kwargs):
    if self.dueDate > self.dateReceived:
        raise ValidationError("dueDate must never be later than dateReceived!")
    super(JobCycle, self).save(*args, **kwargs)

Или, вместо того, чтобы выдать ошибку, вы можете исправить dueDate:

        self.dueDate = self.dateReceieve

Зависит от требуемой логики.

Ошибка валидации происходит из:

from django.core.exceptions import ValidationError

You can override the .clean() method [Django-doc] for this:
class JobCycle(models.Model):
    dateReceived = models.DateField(blank=True, null=True)
    dueDate = models.DateField(blank=True, null=True)
    # ...

    def clean(self):
        super().clean()
        if self.dateReceived and self.dueDate and self.dueDate < self.dateReceived:
            raise ValidationError('Due date cannot be before received date')
This thus renders the model invalid if the due date lies before the received date.
It might however be better to use a DurationField [Django-doc] here, and store a duration instead. For example with:
from django.db.models import DurationField

class JobCycle(models.Model):
    dateReceived = models.DateField(blank=True, null=True)
    duration = models.DurationField()
    # ...
then the due date is simply self.dateReceived + self.duration, and there is no need to validate that.

Note: The save(..) method is not the place to perform validation. The clean(..) method is for that. The save(..) method is to persist the model in the database.
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