在Django模型的空白/空False外键字段中填充默认值

Question

class MyModel(models.Model):
     field1 = models.ForeignKey('AnotherModel', null=False, blank=False)
     field2 = #its a choice field
     # some more fields

What I want is to fill the field1 with a default value if field2 is equal to some specific value (from choice tuple).

I gave it a try by overriding the save() method but I wasn't successful.

def save(self, *args, *kwargs):
   if self.field2 == 'some-specific-value':
      self.field1 = 'some-default-value or a dummy object id?'

For other values of choice field ( field2 ) user has to provide a value but as mentioned above, for a specific value we will fill with default word/string.

I even tried to use signal pre_save , pre_init , post_init but no success

@receiver(post_init, sender=MyModel)
def populate_field1(sender, instance, *args, **kwargs):
    print 'in signal'
    if instance.field2 == 'some-specific-value':
          instance.field1 = 'some-default-value'

How can I do this?

Answer 1

Cleaning is where I would do that if I were you, but I've also seen folks use @property and @func.setter to have it add functionality - so if I set field1, the setter also sets field2 accordingly as it's assigned.

You can do this on cleaning - so if the field is blank=True but not null=True, you can save the field, and cleaning will be where the logic gets executed. This will allow you to save() the model and pass validation (Since blank=True, I can call the save method without erroring, or manually setting it), and my cleaning ensures that the null=False condition is still met by assigning before saving is complete.

class MyModel(models.Model):
     field1 = models.ForeignKey('AnotherModel', null=False, blank=False)
     field2 = #its a choice field
     # some more fields

     def clean(self):
         if self.field2.field == 'value':
             self.field1 = AnotherModel.logic.to.get_the_right_(one)
         else:
             self.field1 = AnotherModel.some_default(value)

Here's an example where I did something similar but with less dependencies:

class Domain(models.Model):
    class Meta:
        ordering = ['domain_name']

    domain_id = models.CharField(max_length=255, unique=True, blank=True)
    domain_name = models.CharField(max_length=255, unique=True)
    domain_arrays = models.ManyToManyField('Array', blank=True)

    def __str__(self):
        return self.domain_name

    def clean(self):
        self.domain_id = self.domain_name.lower().replace('.', '_')
        self.domain_name = self.domain_name.lower()