Export optimizations

Django-import-export isn't smart enough to avoid the fk lookup even if
it only sierializes the fk directly.

[noissue]

(cherry picked from commit 64f7799)

pulp_rpm/app/modelresource.py

@@ -74,6 +74,9 @@ def set_up_queryset(self):
 
         return content
 
+    def dehydrate__pulp_domain(self, content):
+        return str(content._pulp_domain_id)
+
 
 class ModulemdResource(RpmContentResource):
     """
@@ -409,9 +412,13 @@ def set_up_queryset(self):
             UpdateCollections belonging to UpdateRecords for a specified repo-version.
 
         """
-        return UpdateCollection.objects.filter(
-            update_record__in=UpdateRecord.objects.filter(pk__in=self.repo_version.content)
-        ).order_by("pulp_id")
+        return (
+            UpdateCollection.objects.filter(
+                update_record__in=UpdateRecord.objects.filter(pk__in=self.repo_version.content)
+            )
+            .order_by("pulp_id")
+            .select_related("update_record")
+        )
 
     class Meta:
         model = UpdateCollection
@@ -438,9 +445,13 @@ def set_up_queryset(self):
             UpdateReferences belonging to UpdateRecords for a specified repo-version.
 
         """
-        return UpdateReference.objects.filter(
-            update_record__in=UpdateRecord.objects.filter(pk__in=self.repo_version.content)
-        ).order_by("pulp_id")
+        return (
+            UpdateReference.objects.filter(
+                update_record__in=UpdateRecord.objects.filter(pk__in=self.repo_version.content)
+            )
+            .order_by("pulp_id")
+            .select_related("update_record")
+        )
 
     class Meta:
         model = UpdateReference
@@ -529,6 +540,7 @@ def set_up_queryset(self):
             )
             .distinct("name", "epoch", "version", "release", "arch")
             .order_by("name", "epoch", "version", "release", "arch")
+            .select_related("update_collection", "update_collection__update_record")
         )
 
     class Meta: