Question

I have a model:

class picture(models.Model):
    name = models.CharField(null=False, blank=False, max_length=128)
    collections = models.ManyToManyField('collection', null=False, blank=False)
    sizes = models.ManyToManyField('picture_size', null=False, blank=False)
    papers = models.ManyToManyField('picture_paper', null=False, blank=False)
    base_price = models.DecimalField(decimal_places=2, null=False, blank=False, default=2000, max_digits=10)
    img_icon = models.FileField(blank=False, null=False, upload_to='pic_icons')
    img_large = models.FileField(blank=False, null=False, upload_to='pic_large')
    img_huge = models.FileField(blank=False, null=False, upload_to='pic_huge')
    is_active = models.BooleanField(blank=False, null=False, default=True)

and picture_paper:

class picture_paper(models.Model):
    name = models.CharField(null=False, blank=False, max_length=128)
    price_per_ssm = models.DecimalField(null=False, blank=False, decimal_places=2, max_digits=10)
    is_active = models.BooleanField(null=False, blank=False, default=True)

I register them models in admin and can create a picture_paper but can’t delete it:

(1054, “Unknown column ‘picture_paper_id’ in ‘where clause'”)

The SQL it is building is this:

'DELETE FROM `core_picture_papers` WHERE `picture_paper_id` IN (%s)'

explain core_picture_papers:

id  int(11) NO  PRI     auto_increment
picture_id  int(11) NO  MUL     
paper_id    int(11) NO  MUL 

Is my model setup totally wrong (I’m trying to build a dictionary of paper kinds and hook them to pictures – a picture can relate to a few sizes or one etc)? Or there is something I’m missing?

Answer 1

I would say that you’re trying to remove a picture_paper object that is related to an existing picture object. As your M2M can’t be Null or Blank, you get an error when you’re trying to remove it.

Take a look to the Django documentation about on_delete parameter. You will probably need to set it as PROTECTED and handle the exceptions properly.