MPTT - How to override “tree_id”

Question

I want to override the tree_id field as following:

Given:

class Thing(MPTTModel):
    thing_id = models.AutoField(primary_key=True)
    ...

    class MPTTMeta:
        tree_id = ?

While creating the "Thing" first parent I want to initiate tree_id with the thing_id assigned when object is firstly saved.

Next, for "Thing" objects created later I want to pass the thing_id of the first parent created earlier.

i.e. all the nodes at tree will have as tree_id the objectId(thing_id) of the first ancestor.

Is it possible?

How have I to pass the value while creating the "Thing" objects?

Edit:

So it seems the solution for my needs is merely: Thing.objects.get(pk=thing_id).get_descendants()

Answer 1

I don't know what you're trying to do. tree_id is a django-mptt internal field, it doesn't have much meaning outside the mptt algorithm.

Maybe you're trying to sort your tree by thing_id, so that things with oldest ancestors appear first in the tree? I don't know why you'd want to do that, but if so you should probably use order_insertion_by.

class MPTTMeta:
    order_insertion_by = ['thing_id']

Docs: http://django-mptt.github.com/django-mptt/models.html#model-options