[PATCH 07/10] REST: De-duplicate handling of nested resource URLs

[Stephen Finucane]

These were all doing the same thing. Make things more generic.

We also speed up test (inadvertently) by using the 'patch_id' attribute
of the 'Check' model rather than 'patch.id', thus avoiding the JOIN.

Signed-off-by: Stephen Finucane <stephen at that.guru>
---
 patchwork/api/base.py             | 52 +++++++++----------------------
 patchwork/api/check.py            | 10 ++++--
 patchwork/api/embedded.py         | 28 +++++++++++++----
 patchwork/tests/api/test_event.py |  2 +-
 4 files changed, 45 insertions(+), 47 deletions(-)

diff --git patchwork/api/base.py patchwork/api/base.py
index 3ed4182c..0f5c44a2 100644
--- patchwork/api/base.py
+++ patchwork/api/base.py
@@ -9,8 +9,8 @@ from django.conf import settings
 from django.shortcuts import get_object_or_404
 from rest_framework import permissions
 from rest_framework.pagination import PageNumberPagination
+from rest_framework.relations import HyperlinkedIdentityField
 from rest_framework.response import Response
-from rest_framework.serializers import HyperlinkedIdentityField
 from rest_framework.serializers import HyperlinkedModelSerializer
 from rest_framework.utils.urls import replace_query_param
 
@@ -122,52 +122,28 @@ class MultipleFieldLookupMixin(object):
         return get_object_or_404(queryset, **filter_kwargs)
 
 
-class CheckHyperlinkedIdentityField(HyperlinkedIdentityField):
-    def get_url(self, obj, view_name, request, format):
-        # Unsaved objects will not yet have a valid URL.
-        if obj.pk is None:
-            return None
-
-        return self.reverse(
-            view_name,
-            kwargs={
-                'patch_id': obj.patch.id,
-                'check_id': obj.id,
-            },
-            request=request,
-            format=format,
-        )
+class NestedHyperlinkedIdentityField(HyperlinkedIdentityField):
+    """A variant of HyperlinkedIdentityField that supports nested resources."""
 
+    def __init__(self, view_name, lookup_field_mapping, **kwargs):
+        self.lookup_field_mapping = lookup_field_mapping
+        super().__init__(view_name, **kwargs)
 
-class CoverCommentHyperlinkedIdentityField(HyperlinkedIdentityField):
     def get_url(self, obj, view_name, request, format):
         # Unsaved objects will not yet have a valid URL.
-        if obj.pk is None:
+        if hasattr(obj, 'pk') and obj.pk in (None, ''):
             return None
 
-        return self.reverse(
-            view_name,
-            kwargs={
-                'cover_id': obj.cover.id,
-                'comment_id': obj.id,
-            },
-            request=request,
-            format=format,
-        )
-
-
-class PatchCommentHyperlinkedIdentityField(HyperlinkedIdentityField):
-    def get_url(self, obj, view_name, request, format):
-        # Unsaved objects will not yet have a valid URL.
-        if obj.pk is None:
-            return None
+        kwargs = {}
+        for (
+            lookup_url_kwarg,
+            lookup_field,
+        ) in self.lookup_field_mapping.items():
+            kwargs[lookup_url_kwarg] = getattr(obj, lookup_field)
 
         return self.reverse(
             view_name,
-            kwargs={
-                'patch_id': obj.patch.id,
-                'comment_id': obj.id,
-            },
+            kwargs=kwargs,
             request=request,
             format=format,
         )
diff --git patchwork/api/check.py patchwork/api/check.py
index c28d89f7..f5461fc6 100644
--- patchwork/api/check.py
+++ patchwork/api/check.py
@@ -14,8 +14,8 @@ from rest_framework.serializers import HiddenField
 from rest_framework.serializers import HyperlinkedModelSerializer
 from rest_framework.serializers import ValidationError
 
-from patchwork.api.base import CheckHyperlinkedIdentityField
 from patchwork.api.base import MultipleFieldLookupMixin
+from patchwork.api.base import NestedHyperlinkedIdentityField
 from patchwork.api.base import CurrentPatchDefault
 from patchwork.api.embedded import UserSerializer
 from patchwork.api.filters import CheckFilterSet
@@ -25,7 +25,13 @@ from patchwork.models import Patch
 
 class CheckSerializer(HyperlinkedModelSerializer):
 
-    url = CheckHyperlinkedIdentityField('api-check-detail')
+    url = NestedHyperlinkedIdentityField(
+        'api-check-detail',
+        lookup_field_mapping={
+            'patch_id': 'patch_id',
+            'check_id': 'id',
+        },
+    )
     patch = HiddenField(default=CurrentPatchDefault())
     user = UserSerializer(default=CurrentUserDefault())
 
diff --git patchwork/api/embedded.py patchwork/api/embedded.py
index 485ed6f7..7105da08 100644
--- patchwork/api/embedded.py
+++ patchwork/api/embedded.py
@@ -16,9 +16,7 @@ from rest_framework.serializers import PrimaryKeyRelatedField
 from rest_framework.serializers import SerializerMethodField
 
 from patchwork.api.base import BaseHyperlinkedModelSerializer
-from patchwork.api.base import CheckHyperlinkedIdentityField
-from patchwork.api.base import CoverCommentHyperlinkedIdentityField
-from patchwork.api.base import PatchCommentHyperlinkedIdentityField
+from patchwork.api.base import NestedHyperlinkedIdentityField
 from patchwork import models
 
 
@@ -82,7 +80,13 @@ class WebURLMixin(BaseHyperlinkedModelSerializer):
 class CheckSerializer(SerializedRelatedField):
     class _Serializer(BaseHyperlinkedModelSerializer):
 
-        url = CheckHyperlinkedIdentityField('api-check-detail')
+        url = NestedHyperlinkedIdentityField(
+            'api-check-detail',
+            lookup_field_mapping={
+                'patch_id': 'patch_id',
+                'check_id': 'id',
+            },
+        )
 
         def to_representation(self, instance):
             data = super(CheckSerializer._Serializer, self).to_representation(
@@ -130,7 +134,13 @@ class CoverSerializer(SerializedRelatedField):
 class CoverCommentSerializer(SerializedRelatedField):
     class _Serializer(MboxMixin, WebURLMixin, BaseHyperlinkedModelSerializer):
 
-        url = CoverCommentHyperlinkedIdentityField('api-cover-comment-detail')
+        url = NestedHyperlinkedIdentityField(
+            'api-cover-comment-detail',
+            lookup_field_mapping={
+                'cover_id': 'cover_id',
+                'comment_id': 'id',
+            },
+        )
 
         class Meta:
             model = models.CoverComment
@@ -182,7 +192,13 @@ class PatchSerializer(SerializedRelatedField):
 class PatchCommentSerializer(SerializedRelatedField):
     class _Serializer(MboxMixin, WebURLMixin, BaseHyperlinkedModelSerializer):
 
-        url = PatchCommentHyperlinkedIdentityField('api-patch-comment-detail')
+        url = NestedHyperlinkedIdentityField(
+            'api-patch-comment-detail',
+            lookup_field_mapping={
+                'patch_id': 'patch_id',
+                'comment_id': 'id',
+            },
+        )
 
         class Meta:
             model = models.PatchComment
diff --git patchwork/tests/api/test_event.py patchwork/tests/api/test_event.py
index 7ca09c2e..1a0d811d 100644
--- patchwork/tests/api/test_event.py
+++ patchwork/tests/api/test_event.py
@@ -200,7 +200,7 @@ class TestEventAPI(APITestCase):
         for _ in range(3):
             self._create_events()
 
-        with self.assertNumQueries(33):
+        with self.assertNumQueries(30):
             self.client.get(self.api_url())
 
     def test_order_by_date_default(self):
-- 
2.37.3