CODEWITHSUNDEEP
djangodjango-models
Aleksei Khatkevich
Aleksei Khatkevich

Reputation: 2197

How to make "default" in model field pick-up data of the other model's field when entry is created?

I have a following model:

class BoatImage(models.Model):

    boat_photo = models.ImageField(upload_to=get_timestamp_path, blank=True,
                                   verbose_name='Boat photo', )
    boat = models.ForeignKey("BoatModel",  on_delete=models.SET_NULL, verbose_name="Boat ForeignKey",  null=True)
    memory = models.PositiveSmallIntegerField(blank=True, null=True, default = ???)

goal is to when entry is made, default in “memory” field should pick up “boat’ field ID or PK and save it the memory “field”, that is, id in both fields should coincide. I am trying to use default with method like:

def funk(self):
    return self.boat.id # or self.boat.pk or self.boat_id – no difference

But it says – funk should return int, not foreignkey(error)

Question is how to store foreignkey id of the “boat” field in “memory” field when entry is created???

It is possible to do it in save() method but it is quite non-elegant solution in my opinion.

Thanks...

implementation via save()

    def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
        if self.boat and not self.memory:  # save
            self.memory = self.boat_id
        elif not self.boat and self.memory:  # restore
            self.boat_id = self.memory
        elif self.boat and self.memory and self.boat_id != self.memory:  # correct
            self.memory = self.boat_id
        models.Model.save(self, force_insert=False, force_update=False, using=None,
                          update_fields=None)

Upvotes: 0

Views: 39

Answers (1)

chirag soni
chirag soni

Reputation: 1026

As per my unserstanding, you can do one thing first save the model with 

default=0

for the memory field then to assign the id run an update query

Upvotes: 1

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