[FIXED] how to set a default value for a field model to another model field

Issue

here are models.py file

class album(TimeStampedModel):
    #album_artist = models.ForeignKey(artist, on_delete=models.CASCADE)
    album_name = models.CharField(max_length=100, default="New Album")
    #released_at = models.DateTimeField(blank=False, null=False)
    #price = models.DecimalField(
     #   max_digits=6, decimal_places=2, blank=False, null=False)
    #is_approved = models.BooleanField(
     #   default=False, blank=False)

    #def __str__(self):
    #    return self.album_name


class song(models.Model):
    name = models.CharField(max_length=100,blank=True,null=False)
    album = models.ForeignKey(album, on_delete=models.CASCADE,default=None)
    # image = models.ImageField(upload_to='images/', blank = False)
    # thumb = ProcessedImageField(upload_to = 'thumbs/', format='JPEG')
    # audio = models.FileField(
        # upload_to='audios/', validators=[FileExtensionValidator(['mp3', 'wav'])])
    # def __str__(self):
        # return self.name

I want to make the default value of the song name equal to the album name which i choose by the album Foreignkey. (in the admin panel page) any help ?

Solution

Provided the song name is set to blank=True. You can create a pre_save signal to set the name.

...

from django.db.models.signals import pre_save
from django.dispatch import receiver

....

@receiver(pre_save, sender=Song)
def song_pre_save(sender, instance, **kwargs):
    if instance.name is None:
        album = Album.object.get(pk=instance.album)
        instance.name = album.album_name
  

You can read more on the Django website

Answered By - theeomm