TreeNodeModel is incompatible with UUID primary keys (default=uuid4): new nodes never initialize _path/_depth, get_descendants() returns the whole table

[RiON69]

Environment

• django-fast-treenode: 3.2.10
• Django: 5.2 / 6.0
• Database: PostgreSQL (also reproducible on SQLite)
• Python: 3.13

Model

import uuid
from django.db import models
from treenode.models import TreeNodeModel


class Department(TreeNodeModel):
    id = models.UUIDField(primary_key=True, editable=False, default=uuid.uuid4)
    name = models.CharField(max_length=100)

Steps to reproduce

root = Department.objects.create(name="Root")
child = Department.objects.create(name="Child", parent=root)

root.refresh_from_db(); child.refresh_from_db()
print(repr(root._path), repr(child._path))   # -> '' ''  (expected: '000', '000.000')

# With ~N unrelated rows in the table:
root.get_descendants_queryset(include_self=True).count()
# -> N (the ENTIRE table; `_path__startswith('')` matches everything)

Every save() also logs:

ERROR TreeNodeModel save error: object with pk 45bdfedb-... not found in DB

Root cause

1. New-node detection. TreeNodeModel.save() decides whether a node is new via
   if self.pk: (models.py#L192).
   With UUIDField(default=uuid4) the pk is populated before the INSERT, so a brand-new
   instance always takes the "existing node" branch:

   • get_db_state() finds nothing → the save error log above;
   • the is_new branch never runs → _path/_depth are never generated,
     siblings are never shifted, no path-rebuild task is enqueued.

2. PK assignment. The is_new branch does self.pk = self.db.get_next_id(), and
   SQLService.get_next_id() assumes an integer, database-generated pk
   (nextval('{table}_id_seq') on PostgreSQL, MAX(id)+1 on SQLite/MySQL) — this can
   never work for UUID pks, so even forcing the branch (pk=None) breaks.

3. (secondary) Raw-SQL helpers (RawSQLMixin.refresh(), get_db_state()) query
   WHERE id = %s with the Python uuid.UUID value. On SQLite the stored value is a
   32-char hex string without dashes, so the query never matches (e.g. refresh()
   crashes with TypeError: cannot unpack non-iterable NoneType object inside
   get_descendants_queryset() → get_order()).

Consequences

• _path/_depth stay ''/0 for every node created through the ORM;
• get_descendants*() filters _path__startswith('') and returns every row in the
  table (silently wrong data, cross-tenant leakage in multi-tenant apps);
• add_child() / insert_at() positioning is a no-op (no sibling shift, no renormalization);
• constant ERROR log spam on every save().

Suggested fix

• Detect newness with self._state.adding instead of if self.pk: — works for any pk type;
• only call get_next_id() when self.pk is None (keep application-assigned pks intact).

Happy to submit a PR if the approach sounds right.

Workaround we use meanwhile

class UUIDTreeNodeModel(TreeNodeModel):
    class Meta:
        abstract = True

    def save(self, *args, **kwargs):
        model = self._meta.model
        is_new = self._state.adding
        is_move = is_shift = False
        old_parent_id = None

        if not is_new:
            state = self.get_db_state()
            if state:
                is_shift = self.priority != state["priority"]
                is_move = self.parent_id != state["parent_id"]
                old_parent_id = state["parent_id"]

        if is_new:
            if self.priority is None:
                self.priority = BASE - 1
            self._path = self.generate_path()
            self._depth = self._path.count(".")

        if (is_new or is_move) and self.priority is not None:
            self._shift_siblings_forward()

        models.Model.save(self, *args, **kwargs)

        if is_new or is_move or is_shift:
            if is_move:
                model.tasks.add("update", old_parent_id)
            model.tasks.add("update", self.parent_id)
            model.tasks.run()
            self.clear_cache()