Question

I learning python and django and trying to make some sort of simple forum. I created models:

class Board(models.Model):
    title = models.CharField(max_length=200)
    description = models.TextField(blank = True)

class Post(models.Model):
    board = models.ForeignKey(Board)
    ...

I’d like to have post numeration starting from 0 for every board. How i should change my models to achieve that? What am i doing wrong?

Answer 1

I don’t know if you’re talking about using the primary key as the post ID, but that won’t work if you want it to start with 0 for each board. I’d recommend adding another field on your Post model and manage it yourself on the save method. Example:

class Post(models.Model):
    board = models.ForeignKey(Board)
    post_count = models.PositiveIntegerField(default=0)

    def save(self, *args, **kwargs):
        if not self.id:
            self.post_count = self.board.post_set.count()
        super(Post, self).save(*args, **kwargs)

Edit: As Brian points out, there could be problems when posts are deleted. This would result in duplicate post_ids. You could add a deleted field to the model to “fake” delete posts (don’t show when deleted = True) which would keep the post_id counting accurate.

Edit 2: You could set the post_count to be equal to the maximum post count for this board + 1 (or 0 if the count is 0)