Add custom serializers for "_artifact" vs "_artifacts"

Remove boilerplate from the plugins by defining new, more specialized
serializers for the single-artifact-per-content case, the
multiple-artifacts-per-content case, and the no-artifacts-per-content
case.

Required PR: pulp/pulp_file#159
Required PR: pulp/pulp-smash#1164
Required PR: pulp/pulpcore-plugin#38

re: #4366
https://pulp.plan.io/issues/4366

pulpcore/app/serializers/__init__.py

@@ -14,7 +14,12 @@
     AsyncOperationResponseSerializer
 )
 from .fields import BaseURLField, ContentRelatedField, LatestVersionField  # noqa
-from .content import ArtifactSerializer, ContentSerializer  # noqa
+from .content import (  # noqa
+    ArtifactSerializer,
+    NoArtifactContentSerializer,
+    SingleArtifactContentSerializer,
+    MultipleArtifactContentSerializer,
+)
 from .progress import ProgressReportSerializer  # noqa
 from .publication import (  # noqa
     ContentGuardSerializer,

pulpcore/app/serializers/content.py

@@ -11,9 +11,32 @@
 UNIQUE_ALGORITHMS = ['sha256', 'sha384', 'sha512']
 
 
-class ContentSerializer(base.MasterModelSerializer):
+class BaseContentSerializer(base.MasterModelSerializer):
     _href = base.DetailIdentityField()
 
+    class Meta:
+        model = models.Content
+        fields = base.MasterModelSerializer.Meta.fields
+
+
+class NoArtifactContentSerializer(BaseContentSerializer):
+
+    class Meta:
+        model = models.Content
+        fields = base.MasterModelSerializer.Meta.fields
+
+
+class SingleArtifactContentSerializer(BaseContentSerializer):
+    _artifact = fields.SingleContentArtifactField(
+        help_text=_("Artifact file representing the physical content"),
+    )
+
+    class Meta:
+        model = models.Content
+        fields = base.MasterModelSerializer.Meta.fields + ('_artifact',)
+
+
+class MultipleArtifactContentSerializer(BaseContentSerializer):
     _artifacts = fields.ContentArtifactsField(
         help_text=_("A dict mapping relative paths inside the Content to the corresponding"
                     "Artifact URLs. E.g.: {'relative/path': "

pulpcore/app/serializers/fields.py

@@ -17,6 +17,39 @@ class ContentRelatedField(DetailRelatedField):
     queryset = models.Content.objects.all()
 
 
+class SingleContentArtifactField(RelatedField):
+    """
+    A serializer field for the '_artifacts' ManyToManyField on the Content model (single-artifact).
+    """
+    lookup_field = 'pk'
+    view_name = 'artifacts-detail'
+    queryset = models.Artifact.objects.all()
+    allow_null = True
+
+    def get_attribute(self, instance):
+        """
+        Returns the field from the instance that should be serialized using this serializer field.
+
+        This serializer looks up the list of artifacts and returns only one, if any exist. If more
+        than one exist, it throws and exception because this serializer is being used in an
+        improper context.
+
+        Args:
+            instance (:class:`pulpcore.app.models.Content`): An instance of Content being
+                serialized.
+
+        Returns:
+            A single Artifact model related to the instance of Content.
+        """
+        try:
+            return instance._artifacts.get()
+        except models.Artifact.DoesNotExist:
+            return None
+        except models.Artifact.MultipleObjectsReturned:
+            raise ValueError(_("SingleContentArtifactField should not be used in a context where "
+                               "multiple artifacts for one content is possible."))
+
+
 class ContentArtifactsField(serializers.DictField):
     """
     A serializer field for the '_artifacts' ManyToManyField on the Content model.

pulpcore/app/viewsets/content.py

@@ -6,7 +6,7 @@
 from rest_framework.response import Response
 
 from pulpcore.app.models import Artifact, Content, ContentArtifact
-from pulpcore.app.serializers import ArtifactSerializer, ContentSerializer
+from pulpcore.app.serializers import ArtifactSerializer, MultipleArtifactContentSerializer
 from pulpcore.app.viewsets.base import BaseFilterSet, NamedModelViewSet
 
 from .custom_filters import (
@@ -80,7 +80,6 @@ class ContentFilter(BaseFilterSet):
     class Meta:
         model = Content
         fields = {
-            '_type': ['exact', 'in'],
             'repository_version': ['exact'],
             'repository_version_added': ['exact'],
             'repository_version_removed': ['exact'],
@@ -92,9 +91,10 @@ class ContentViewSet(NamedModelViewSet,
                      mixins.RetrieveModelMixin,
                      mixins.ListModelMixin):
     endpoint_name = 'content'
-    queryset = Content.objects.all()
-    serializer_class = ContentSerializer
     filterset_class = ContentFilter
+    # These are just placeholders, the plugin writer would replace them with the actual
+    queryset = Content.objects.all()
+    serializer_class = MultipleArtifactContentSerializer
 
     @transaction.atomic
     def create(self, request):

pulpcore/tests/functional/api/using_plugin/test_orphans.py

@@ -79,7 +79,7 @@ def test_clean_orphan_content_unit(self):
         )
 
         # Verify that the artifact is present on disk.
-        artifact_path = self.api_client.get(content['artifact'])['file']
+        artifact_path = self.api_client.get(content['_artifact'])['file']
         cmd = ('ls', artifact_path)
         self.cli_client.run(cmd, sudo=True)
 

pulpcore/tests/functional/api/using_plugin/test_repo_versions.py

@@ -324,7 +324,7 @@ def test_delete_first_version(self):
             get_content(self.repo, self.repo_version_hrefs[0])
         for repo_version_href in self.repo_version_hrefs[1:]:
             artifact_paths = get_artifact_paths(self.repo, repo_version_href)
-            self.assertIn(self.content[0]['artifact'], artifact_paths)
+            self.assertIn(self.content[0]['_artifact'], artifact_paths)
 
     def test_delete_last_version(self):
         """Delete the last repository version.
@@ -346,8 +346,8 @@ def test_delete_last_version(self):
         self.repo = self.client.get(self.repo['_href'])
         artifact_paths = get_artifact_paths(self.repo)
 
-        self.assertNotIn(self.content[-2]['artifact'], artifact_paths)
-        self.assertIn(self.content[-1]['artifact'], artifact_paths)
+        self.assertNotIn(self.content[-2]['_artifact'], artifact_paths)
+        self.assertIn(self.content[-1]['_artifact'], artifact_paths)
 
     def test_delete_middle_version(self):
         """Delete a middle version."""
@@ -359,7 +359,7 @@ def test_delete_middle_version(self):
 
         for repo_version_href in self.repo_version_hrefs[index + 1:]:
             artifact_paths = get_artifact_paths(self.repo, repo_version_href)
-            self.assertIn(self.content[index]['artifact'], artifact_paths)
+            self.assertIn(self.content[index]['_artifact'], artifact_paths)
 
     def test_delete_publication(self):
         """Delete a publication.

pulpcore/tests/unit/content/test_handler.py

@@ -13,9 +13,9 @@ class HandlerSaveContentTestCase(TestCase):
 
     def setUp(self):
         self.f1 = FileContent.objects.create(relative_path='f1', digest='1')
-        self.f1.artifact = None
+        ContentArtifact.objects.create(artifact=None, content=self.f1, relative_path='f1')
         self.f2 = FileContent.objects.create(relative_path='f2', digest='1')
-        self.f2.artifact = None
+        ContentArtifact.objects.create(artifact=None, content=self.f2, relative_path='f2')
 
     def download_result_mock(self, path):
         dr = Mock()