Django MPTT duplicate key value violates unique constraint

Question

I practice django-mptt and face problem

Here is my models.py

class Genre(MPTTModel):
    name = models.CharField(max_length=50, unique=True)
    parent = TreeForeignKey('self', null=True, blank=True, related_name='children', db_index=True)

I create some data :

USA
- NY
  - BuildingA
    - 3F
    - 4F
  - BuildingB

And now,I need to create 4F under BuildingB

floor3 = Genre.objects.create(name="3F", parent= buildingB)

but face problem :

IntegrityError: duplicate key value violates unique constraint "myapp_genre_name_key"
DETAIL:  Key (name)=(3F) already exists.

How can I fix it??

Do you really need the `unique=True` argument? It's the key of your problem. — Alex Morozov, Feb 02 '16 at 14:11
Thank god, your are right !! I originally thought it was because the ````MPTTMeta````:````order_insertion_by = ['name']````. Do you know what is ````order_insertion_by = ['name']```` — user2492364, Feb 02 '16 at 14:13
It's a default ordering for newly inserted items. If you order them by hand, this option will no be of great help to you. — Alex Morozov, Feb 02 '16 at 14:15

score 0 · Accepted Answer · answered Feb 02 '16 at 14:14

In my understanding, you want your names to be unique across the building. To achieve that, remove the unique=True from the name field declaration and add a Meta option:

class Genre(MPTTModel):
    name = models.CharField(max_length=50)
    parent = TreeForeignKey('self', null=True, blank=True, related_name='children', db_index=True)

    class Meta:
        unique_together = (('name', 'parent', ), )

Django MPTT duplicate key value violates unique constraint

1 Answers1