Ensure the correct Taxonomy subclass is used

openedx_tagging/core/tagging/api.py

@@ -10,7 +10,7 @@
 Please look at the models.py file for more information about the kinds of data
 are stored in this app.
 """
-from typing import List, Type
+from typing import List, Type, Union
 
 from django.db.models import QuerySet
 from django.utils.translation import gettext_lazy as _
@@ -45,12 +45,19 @@ def get_taxonomies(enabled=True) -> QuerySet:
     If you want the disabled taxonomies, pass enabled=False.
     If you want all taxonomies (both enabled and disabled), pass enabled=None.
     """
-    queryset = Taxonomy.objects.order_by("name", "id")
+    queryset = Taxonomy.objects.order_by("name", "id").select_subclasses()
     if enabled is None:
         return queryset.all()
     return queryset.filter(enabled=enabled)
 
 
+def get_taxonomy(id: int) -> Union[Taxonomy, None]:
+    """
+    Returns a Taxonomy of the appropriate subclass which has the given ID.
+    """
+    return Taxonomy.objects.filter(id=id).select_subclasses().first()
+
+
 def get_tags(taxonomy: Taxonomy) -> List[Tag]:
     """
     Returns a list of predefined tags for the given taxonomy.
@@ -87,8 +94,8 @@ def get_object_tags(
     Pass valid_only=False when displaying tags to content authors, so they can see invalid tags too.
     Invalid tags will likely be hidden from learners.
     """
-    tags = ObjectTag.objects.filter(
-        taxonomy=taxonomy, object_id=object_id, object_type=object_type
+    tags = taxonomy.objecttag_set.filter(
+        object_id=object_id, object_type=object_type
     ).order_by("id")
     return [tag for tag in tags if not valid_only or taxonomy.validate_object_tag(tag)]
 

openedx_tagging/core/tagging/migrations/0002_systemtaxonomy.py

@@ -0,0 +1,30 @@
+# Generated by Django 3.2.19 on 2023-06-28 10:19
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("oel_tagging", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="SystemTaxonomy",
+            fields=[
+                (
+                    "taxonomy_ptr",
+                    models.OneToOneField(
+                        auto_created=True,
+                        on_delete=django.db.models.deletion.CASCADE,
+                        parent_link=True,
+                        primary_key=True,
+                        serialize=False,
+                        to="oel_tagging.taxonomy",
+                    ),
+                ),
+            ],
+            bases=("oel_tagging.taxonomy",),
+        ),
+    ]

openedx_tagging/core/tagging/migrations/0003_objecttag__taxonomy.py

@@ -0,0 +1,28 @@
+# Generated by Django 3.2.19 on 2023-07-04 02:20
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("oel_tagging", "0002_systemtaxonomy"),
+    ]
+
+    operations = [
+        migrations.RemoveIndex(
+            model_name="objecttag",
+            name="oel_tagging_taxonom_3668ec_idx",
+        ),
+        migrations.RenameField(
+            model_name="objecttag",
+            old_name="taxonomy",
+            new_name="_taxonomy",
+        ),
+        migrations.AddIndex(
+            model_name="objecttag",
+            index=models.Index(
+                fields=["_taxonomy", "_value"], name="oel_tagging__taxono_af4c8a_idx"
+            ),
+        ),
+    ]

openedx_tagging/core/tagging/models.py

@@ -3,10 +3,10 @@
 
 from django.db import models
 from django.utils.translation import gettext_lazy as _
+from model_utils.managers import InheritanceManager
 
 from openedx_learning.lib.fields import MultiCollationTextField, case_insensitive_char_field
 
-
 # Maximum depth allowed for a hierarchical taxonomy's tree of tags.
 TAXONOMY_MAX_DEPTH = 3
 
@@ -93,11 +93,19 @@ def get_lineage(self) -> Lineage:
         return lineage
 
 
+class TaxonomyManager(InheritanceManager):
+    """
+    Base Taxonomy class uses InheritanceManager to help instantiate subclasses during queries.
+    """
+
+
 class Taxonomy(models.Model):
     """
     Represents a namespace and rules for a group of tags which can be applied to a particular Open edX object.
     """
 
+    objects = TaxonomyManager()
+
     id = models.BigAutoField(primary_key=True)
     name = case_insensitive_char_field(
         null=False,
@@ -140,6 +148,18 @@ class Taxonomy(models.Model):
     class Meta:
         verbose_name_plural = "Taxonomies"
 
+    def __repr__(self):
+        """
+        Developer-facing representation of a Taxonomy.
+        """
+        return str(self)
+
+    def __str__(self):
+        """
+        User-facing string representation of a Taxonomy.
+        """
+        return f"<{self.__class__.__name__}> {self.name}"
+
     @property
     def system_defined(self) -> bool:
         """
@@ -204,7 +224,7 @@ def validate_object_tag(
         """
         # Must be linked to this taxonomy
         if check_taxonomy and (
-            not object_tag.taxonomy_id or object_tag.taxonomy_id != self.id
+            not object_tag.taxonomy or object_tag.taxonomy.id != self.id
         ):
             return False
 
@@ -241,8 +261,8 @@ def tag_object(
 
         current_tags = {
             tag.tag_ref: tag
-            for tag in ObjectTag.objects.filter(
-                taxonomy=self, object_id=object_id, object_type=object_type
+            for tag in self.objecttag_set.filter(
+                object_id=object_id, object_type=object_type
             )
         }
         updated_tags = []
@@ -310,7 +330,7 @@ class ObjectTag(models.Model):
         max_length=255,
         help_text=_("Type of object being tagged"),
     )
-    taxonomy = models.ForeignKey(
+    _taxonomy = models.ForeignKey(
         Taxonomy,
         null=True,
         default=None,
@@ -348,9 +368,57 @@ class ObjectTag(models.Model):
 
     class Meta:
         indexes = [
-            models.Index(fields=["taxonomy", "_value"]),
+            models.Index(fields=["_taxonomy", "_value"]),
         ]
 
+    def __init__(self, *args, **kwargs):
+        """
+        Initializes the cached taxonomy instance.
+        """
+        super().__init__(*args, **kwargs)
+        self._cached_taxonomy = None
+
+    def __repr__(self):
+        """
+        Developer-facing representation of an ObjectTag.
+        """
+        return str(self)
+
+    def __str__(self):
+        """
+        User-facing string representation of an ObjectTag.
+        """
+        return f"{self.object_id} ({self.object_type}): {self.name}={self.value}"
+
+    @property
+    def taxonomy(self) -> str:
+        """
+        Returns this tag's taxonomy object, instantiated as the correct Taxonomy subclass.
+
+        This instance is cached so that subsequent calls to self.taxonomy don't re-fetch the value.
+
+        Returns None if taxonomy_id is not set.
+        """
+        if not self._taxonomy_id:
+            self._cached_taxonomy = None
+
+        elif not self._cached_taxonomy:
+            self._cached_taxonomy = (
+                Taxonomy.objects.filter(id=self._taxonomy_id)
+                .select_subclasses()
+                .first()
+            )
+
+        return self._cached_taxonomy
+
+    @taxonomy.setter
+    def taxonomy(self, taxonomy: Taxonomy):
+        """
+        Stores to the _taxonomy field.
+        """
+        self._taxonomy = taxonomy
+        self._cached_taxonomy = taxonomy
+
     @property
     def name(self) -> str:
         """
@@ -359,7 +427,7 @@ def name(self) -> str:
         If taxonomy is set, then returns its name.
         Otherwise, returns the cached _name field.
         """
-        return self.taxonomy.name if self.taxonomy_id else self._name
+        return self.taxonomy.name if self._taxonomy_id else self._name
 
     @name.setter
     def name(self, name: str):
@@ -402,7 +470,9 @@ def is_valid(self) -> bool:
 
         A valid ObjectTag must be linked to a Taxonomy, and be a valid tag in that taxonomy.
         """
-        return self.taxonomy_id and self.taxonomy.validate_object_tag(self)
+        if self._taxonomy_id:
+            return self.taxonomy.validate_object_tag(self)
+        return False
 
     def get_lineage(self) -> Lineage:
         """
@@ -427,8 +497,10 @@ def resync(self) -> bool:
         changed = False
 
         # Locate a taxonomy matching _name
-        if not self.taxonomy_id:
-            for taxonomy in Taxonomy.objects.filter(name=self.name, enabled=True):
+        if not self._taxonomy_id:
+            for taxonomy in Taxonomy.objects.filter(
+                name=self.name, enabled=True
+            ).select_subclasses():
                 # Make sure this taxonomy will accept object tags like this.
                 self.taxonomy = taxonomy
                 if taxonomy.validate_object_tag(self, check_tag=False):
@@ -456,3 +528,17 @@ def resync(self) -> bool:
             changed = True
 
         return changed
+
+
+class SystemTaxonomy(Taxonomy):
+    """
+    System-defined taxonomies are not editable by normal users; they're defined by fixtures/migrations, and may have
+    dynamically-determined Tags and ObjectTags.
+    """
+
+    @property
+    def system_defined(self) -> bool:
+        """
+        This is a system-defined taxonomy.
+        """
+        return True

openedx_tagging/core/tagging/rules.py

@@ -1,14 +1,20 @@
 """Django rules-based permissions for tagging"""
 
 import rules
+from django.contrib.auth import get_user_model
+
+from .models import ObjectTag, Tag, Taxonomy
+
+User = get_user_model()
+
 
 # Global staff are taxonomy admins.
 # (Superusers can already do anything)
 is_taxonomy_admin = rules.is_staff
 
 
 @rules.predicate
-def can_view_taxonomy(user, taxonomy=None):
+def can_view_taxonomy(user: User, taxonomy: Taxonomy = None) -> bool:
     """
     Anyone can view an enabled taxonomy,
     but only taxonomy admins can view a disabled taxonomy.
@@ -17,7 +23,7 @@ def can_view_taxonomy(user, taxonomy=None):
 
 
 @rules.predicate
-def can_change_taxonomy(user, taxonomy=None):
+def can_change_taxonomy(user: User, taxonomy: Taxonomy = None) -> bool:
     """
     Even taxonomy admins cannot change system taxonomies.
     """
@@ -27,7 +33,7 @@ def can_change_taxonomy(user, taxonomy=None):
 
 
 @rules.predicate
-def can_change_taxonomy_tag(user, tag=None):
+def can_change_taxonomy_tag(user: User, tag: Tag = None) -> bool:
     """
     Even taxonomy admins cannot add tags to system taxonomies (their tags are system-defined), or free-text taxonomies
     (these don't have predefined tags).
@@ -44,7 +50,7 @@ def can_change_taxonomy_tag(user, tag=None):
 
 
 @rules.predicate
-def can_change_object_tag(user, object_tag=None):
+def can_change_object_tag(user: User, object_tag: ObjectTag = None) -> bool:
     """
     Taxonomy admins can create or modify object tags on enabled taxonomies.
     """

requirements/base.in

@@ -6,3 +6,5 @@ Django<5.0                # Web application framework
 djangorestframework<4.0   # REST API
 
 rules<4.0                 # Django extension for rules-based authorization checks
+
+django-model-utils        # InheritanceManager for openedx-tagging models

requirements/base.txt

@@ -10,7 +10,10 @@ django==3.2.19
     # via
     #   -c requirements/constraints.txt
     #   -r requirements/base.in
+    #   django-model-utils
     #   djangorestframework
+django-model-utils==4.3.1
+    # via -r requirements/base.in
 djangorestframework==3.14.0
     # via -r requirements/base.in
 pytz==2023.3

requirements/dev.txt

@@ -78,10 +78,13 @@ django==3.2.19
     #   -c requirements/constraints.txt
     #   -r requirements/quality.txt
     #   django-debug-toolbar
+    #   django-model-utils
     #   djangorestframework
     #   edx-i18n-tools
 django-debug-toolbar==4.1.0
     # via -r requirements/dev.in
+django-model-utils==4.3.1
+    # via -r requirements/quality.txt
 djangorestframework==3.14.0
     # via -r requirements/quality.txt
 docutils==0.20.1

requirements/doc.txt

@@ -41,8 +41,11 @@ django==3.2.19
     # via
     #   -c requirements/constraints.txt
     #   -r requirements/test.txt
+    #   django-model-utils
     #   djangorestframework
     #   sphinxcontrib-django
+django-model-utils==4.3.1
+    # via -r requirements/test.txt
 djangorestframework==3.14.0
     # via -r requirements/test.txt
 doc8==1.1.1

requirements/quality.txt

@@ -47,7 +47,10 @@ django==3.2.19
     # via
     #   -c requirements/constraints.txt
     #   -r requirements/test.txt
+    #   django-model-utils
     #   djangorestframework
+django-model-utils==4.3.1
+    # via -r requirements/test.txt
 djangorestframework==3.14.0
     # via -r requirements/test.txt
 docutils==0.20.1