refactor: drop django-mptt in favour of django-tree-queries

Django-Tree-Queries works with recursive CTEs (common table expressions) to deal
with hierarchical relationships, generally achieving the same result, but without
the `right`, `left` and `tree_id` fields.

Django-MPTT has been unmaintained for several years, and we're suspecting some
subtle bugs in it that we can't really reproduce or verify right now. Anyway it's
a good time to get rid of it.

Note: Some old migrations needed to be changed, as we cannot refer to
MPTT fields anymore. They were essentially regular foreign keys however,
so this won't break the database.

BREAKING! This breaks if Emeis is used as a Django app directly, and depends on
any of the MPTT API / features.

emeis/core/management/commands/create_scope.py

@@ -3,7 +3,6 @@
 from django.core.management.base import BaseCommand
 
 from emeis.core.models import ACL, Role, Scope, User
-from emeis.core.utils import rebuild_mptt_model
 
 
 class Command(BaseCommand):
@@ -78,7 +77,6 @@ def handle(self, *args, **options):
             options["name"] = json.loads(options["name"])
 
         new_scope = Scope.objects.create(name=options["name"], parent=parent)
-        rebuild_mptt_model(Scope)
         out_info["scope_id"] = str(new_scope.pk)
 
         if options["user"]:

emeis/core/migrations/0001_initial.py

@@ -6,7 +6,6 @@
 import django.utils.timezone
 import localized_fields.fields.char_field
 import localized_fields.fields.text_field
-import mptt.fields
 from django.conf import settings
 from django.db import migrations, models
 
@@ -224,7 +223,7 @@ class Migration(migrations.Migration):
                 ),
                 (
                     "parent",
-                    mptt.fields.TreeForeignKey(
+                    models.ForeignKey(
                         blank=True,
                         null=True,
                         on_delete=django.db.models.deletion.SET_NULL,

emeis/core/migrations/0009_alter_scope_parent.py

@@ -1,8 +1,7 @@
 # Generated by Django 3.2.12 on 2022-04-21 07:24
 
-from django.db import migrations
 import django.db.models.deletion
-import mptt.fields
+from django.db import migrations, models
 
 
 class Migration(migrations.Migration):
@@ -14,7 +13,7 @@ class Migration(migrations.Migration):
         migrations.AlterField(
             model_name="scope",
             name="parent",
-            field=mptt.fields.TreeForeignKey(
+            field=models.ForeignKey(
                 blank=True,
                 null=True,
                 on_delete=django.db.models.deletion.CASCADE,

emeis/core/migrations/0010_scope_full_name.py

@@ -1,7 +1,7 @@
 # Generated by Django 3.2.15 on 2022-09-23 09:13
 
-from django.db import migrations
 import localized_fields.fields.char_field
+from django.db import migrations
 
 from emeis.core import models
 

emeis/core/migrations/0011_mptt_to_tree_queries.py

@@ -0,0 +1,45 @@
+# Generated by Django 3.2.25 on 2024-06-03 14:17
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("emeis_core", "0010_scope_full_name"),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name="scope",
+            options={"ordering": ["full_name"]},
+        ),
+        migrations.RemoveField(
+            model_name="scope",
+            name="level",
+        ),
+        migrations.RemoveField(
+            model_name="scope",
+            name="lft",
+        ),
+        migrations.RemoveField(
+            model_name="scope",
+            name="rght",
+        ),
+        migrations.RemoveField(
+            model_name="scope",
+            name="tree_id",
+        ),
+        migrations.AlterField(
+            model_name="scope",
+            name="parent",
+            field=models.ForeignKey(
+                blank=True,
+                null=True,
+                on_delete=django.db.models.deletion.CASCADE,
+                related_name="children",
+                to="emeis_core.scope",
+                verbose_name="parent",
+            ),
+        ),
+    ]

emeis/core/models.py

@@ -10,7 +10,7 @@
 from django.utils import timezone, translation
 from django.utils.translation import gettext_lazy as _
 from localized_fields.fields import LocalizedCharField, LocalizedTextField
-from mptt.models import MPTTModel, TreeForeignKey
+from tree_queries.models import TreeNode, TreeQuerySet
 
 
 def make_uuid():
@@ -158,7 +158,7 @@ def is_authenticated(self):
         return True
 
 
-class Scope(MPTTModel, UUIDModel):
+class Scope(TreeNode, UUIDModel):
     name = LocalizedCharField(_("scope name"), blank=False, null=False, required=False)
 
     full_name = LocalizedCharField(
@@ -168,20 +168,21 @@ class Scope(MPTTModel, UUIDModel):
     description = LocalizedTextField(
         _("scope description"), null=True, blank=True, required=False
     )
-    parent = TreeForeignKey(
-        "self",
-        on_delete=models.CASCADE,
-        null=True,
-        blank=True,
-        related_name="children",
-    )
     is_active = models.BooleanField(default=True)
 
+    objects = TreeQuerySet.as_manager(with_tree_fields=True)
+
+    def save(self, *args, **kwargs):
+        # django-tree-queries does validation in TreeNode.clean(), which is not
+        # called by DRF (only by django forms), so we have to do this here
+        self.clean()
+        return super().save(*args, **kwargs)
+
     def __str__(self):
         return f"{type(self).__name__} ({self.full_name}, pk={self.pk})"
 
     class Meta:
-        ordering = ["full_name"]
+        ordering = ["name"]
 
 
 @receiver(pre_save, sender=Scope)

emeis/core/serializers.py

@@ -33,6 +33,10 @@ class Meta:
 
 
 class MyACLSerializer(BaseSerializer):
+    scope = serializers.ResourceRelatedField(
+        queryset=Scope.objects.all(), required=False, many=False
+    )
+
     included_serializers = {
         "scope": "emeis.core.serializers.ScopeSerializer",
         "role": "emeis.core.serializers.RoleSerializer",
@@ -73,6 +77,22 @@ class Meta:
 
 
 class ScopeSerializer(BaseSerializer):
+    level = serializers.SerializerMethodField()
+
+    def get_level(self, obj):
+        depth = getattr(obj, "tree_depth", None)
+        if depth is not None:
+            return depth
+
+        # Note: This should only happen on CREATE, never in GET (Either list,
+        # detail, or include!) In CREATE, it's a new object that doesn't come
+        # from a QS
+
+        # Sometimes, the model object may come out of a non-django-tree-queries
+        # QS, and thus would not have the `tree_*` attributes amended. Then we
+        # need to go the "slow path"
+        return obj.ancestors().count()
+
     class Meta:
         model = Scope
         fields = BaseSerializer.Meta.fields + (
@@ -83,7 +103,7 @@ class Meta:
             "full_name",
             "is_active",
         )
-        read_only_fields = ["full_name"]
+        read_only_fields = ["full_name", "level"]
 
 
 class PermissionSerializer(BaseSerializer):
@@ -111,6 +131,9 @@ class Meta:
 
 
 class ACLSerializer(BaseSerializer):
+    scope = serializers.ResourceRelatedField(
+        queryset=Scope.objects.all(), required=False, many=False
+    )
     included_serializers = {
         "user": UserSerializer,
         "scope": ScopeSerializer,