feat: Implement ObjectTag retrieve REST API

Retrieve ObjectTags for given Object IDs, and optionally filter by
taxonomy.

openedx_tagging/core/tagging/rest_api/v1/permissions.py

@@ -1,5 +1,5 @@
 """
-Taxonomy permissions
+Tagging permissions
 """
 
 from rest_framework.permissions import DjangoObjectPermissions
@@ -15,3 +15,15 @@ class TaxonomyObjectPermissions(DjangoObjectPermissions):
         "PATCH": ["%(app_label)s.change_%(model_name)s"],
         "DELETE": ["%(app_label)s.delete_%(model_name)s"],
     }
+
+
+class ObjectTagObjectPermissions(DjangoObjectPermissions):
+    perms_map = {
+        "GET": ["%(app_label)s.view_%(model_name)s"],
+        "OPTIONS": [],
+        "HEAD": ["%(app_label)s.view_%(model_name)s"],
+        "POST": ["%(app_label)s.add_%(model_name)s"],
+        "PUT": ["%(app_label)s.change_%(model_name)s"],
+        "PATCH": ["%(app_label)s.change_%(model_name)s"],
+        "DELETE": ["%(app_label)s.delete_%(model_name)s"],
+    }

openedx_tagging/core/tagging/rest_api/v1/serializers.py

@@ -4,7 +4,7 @@
 
 from rest_framework import serializers
 
-from openedx_tagging.core.tagging.models import Taxonomy
+from openedx_tagging.core.tagging.models import Taxonomy, ObjectTag
 
 
 class TaxonomyListQueryParamsSerializer(serializers.Serializer):
@@ -29,3 +29,29 @@ class Meta:
             "system_defined",
             "visible_to_authors",
         ]
+
+
+class ObjectTagListQueryParamsSerializer(serializers.Serializer):
+    """
+    Serializer for the query params for the ObjectTag GET view
+    """
+
+    taxonomy = serializers.PrimaryKeyRelatedField(
+        queryset=Taxonomy.objects.all(), required=False
+    )
+
+
+class ObjectTagSerializer(serializers.ModelSerializer):
+    """
+    Serializer for the ObjectTag model.
+    """
+
+    class Meta:
+        model = ObjectTag
+        fields = [
+            "name",
+            "value",
+            "taxonomy_id",
+            "tag_ref",
+            "is_valid",
+        ]

openedx_tagging/core/tagging/rest_api/v1/urls.py

@@ -10,5 +10,6 @@
 
 router = DefaultRouter()
 router.register("taxonomies", views.TaxonomyView, basename="taxonomy")
+router.register("object_tags", views.ObjectTagView, basename="object_tag")
 
 urlpatterns = [path("", include(router.urls))]

openedx_tagging/core/tagging/rest_api/v1/views.py

@@ -2,15 +2,29 @@
 Tagging API Views
 """
 from django.http import Http404
-from rest_framework.viewsets import ModelViewSet
+from rest_framework import status
+from rest_framework.viewsets import ModelViewSet, ReadOnlyModelViewSet
+from rest_framework.response import Response
+from rest_framework.pagination import PageNumberPagination
 
 from ...api import (
     create_taxonomy,
     get_taxonomy,
     get_taxonomies,
+    get_object_tags,
 )
-from .serializers import TaxonomyListQueryParamsSerializer, TaxonomySerializer
-from .permissions import TaxonomyObjectPermissions
+from .serializers import (
+    TaxonomyListQueryParamsSerializer,
+    TaxonomySerializer,
+    ObjectTagListQueryParamsSerializer,
+    ObjectTagSerializer,
+)
+from .permissions import TaxonomyObjectPermissions, ObjectTagObjectPermissions
+
+
+class ObjectTagPagination(PageNumberPagination):
+    page_size = 100
+    max_page_size = 100
 
 
 class TaxonomyView(ModelViewSet):
@@ -144,3 +158,77 @@ def perform_create(self, serializer):
         Create a new taxonomy.
         """
         serializer.instance = create_taxonomy(**serializer.validated_data)
+
+
+class ObjectTagView(ReadOnlyModelViewSet):
+    """
+    View to retrieve paginated ObjectTags for a provided Object ID (object_id).
+
+    **Retrieve Parameters**
+        * object_id (required): - The Object ID to retrieve ObjectTags for.
+
+    **Retrieve Query Parameters**
+        * taxonomy (optional) - PK of taxonomy to filter ObjectTags for.
+        * page (optional) - Page number of paginated results.
+        * page_size (optional) - Number of results included in each page.
+
+    **Retrieve Example Requests**
+        GET api/tagging/v1/object_tags/:object_id
+        GET api/tagging/v1/object_tags/:object_id?taxonomy=1
+        GET api/tagging/v1/object_tags/:object_id?taxonomy=1&page=2
+        GET api/tagging/v1/object_tags/:object_id?taxonomy=1&page=2&page_size=10
+
+    **Retrieve Query Returns**
+        * 200 - Success
+        * 400 - Invalid query parameter
+        * 403 - Permission denied
+
+    **Create Query Returns**
+        * 403 - Permission denied
+        * 405 - Method not allowed
+
+    **Update Query Returns**
+        * 403 - Permission denied
+        * 405 - Method not allowed
+
+    **Delete Query Returns**
+        * 403 - Permission denied
+        * 405 - Method not allowed
+    """
+
+    serializer_class = ObjectTagSerializer
+    permission_classes = [ObjectTagObjectPermissions]
+    pagination_class = ObjectTagPagination
+    lookup_field = "object_id"
+
+    def get_queryset(self):
+        """
+        Return a queryset of object tags for a given object.
+
+        If a taxonomy is passed in, object tags are limited to that taxonomy.
+        """
+        object_id = self.kwargs.get("object_id")
+        query_params = ObjectTagListQueryParamsSerializer(
+            data=self.request.query_params.dict()
+        )
+        query_params.is_valid(raise_exception=True)
+        taxonomy = query_params.data.get("taxonomy", None)
+        taxonomy = get_taxonomy(taxonomy)
+        return get_object_tags(object_id, taxonomy)
+
+    def retrieve(self, request, object_id=None):
+        """
+        Retrieve ObjectTags that belong to a given object_id and
+        return paginated results.
+
+        Note: We override `retrieve` here instead of `list` because we are
+        passing in the Object ID (object_id) in the path (as opposed to passing
+        it in as a query_param) to retrieve the related ObjectTags.
+        By default retrieve would expect an ObjectTag ID to be passed in the
+        path and returns a it as a single result however that is not
+        behavior we want.
+        """
+        object_tags = self.get_queryset()
+        paginated_object_tags = self.paginate_queryset(object_tags)
+        serializer = ObjectTagSerializer(paginated_object_tags, many=True)
+        return self.get_paginated_response(serializer.data)