Add 404 type response to topic query

server/books/schema/nodes/topic.py

@@ -6,6 +6,11 @@ from graphene_django.filter import DjangoFilterConnectionField
 from books.models import Topic, Module
 from books.schema.nodes import ModuleNode
 
+NOT_FOUND = { 'reason': 'Not Found'}
+
+class NotFound(graphene.ObjectType):
+    reason = graphene.String()
+
 
 class TopicNode(DjangoObjectType):
     pk = graphene.Int()
@@ -27,3 +32,14 @@ class TopicNode(DjangoObjectType):
 
     def resolve_modules(self, *args, **kwargs):
         return Module.get_by_parent(self)
+
+
+class TopicOr404Node(graphene.Union):
+    class Meta:
+        types = (TopicNode, NotFound)
+
+    @classmethod
+    def resolve_type(cls, instance, info):
+        if type(instance).__name__ == "Topic":
+            return TopicNode
+        return NotFound

server/books/schema/queries.py

@@ -5,7 +5,7 @@ from graphene_django.filter import DjangoFilterConnectionField
 from api.utils import get_object
 from core.logger import get_logger
 from .connections import TopicConnection, ModuleConnection
-from .nodes import ContentBlockNode, ChapterNode, ModuleNode, TopicNode, SnapshotNode
+from .nodes import ContentBlockNode, ChapterNode, ModuleNode, NOT_FOUND, TopicNode, SnapshotNode, TopicOr404Node
 from ..models import Book, Topic, Module, Chapter, Snapshot
 
 logger = get_logger(__name__)
@@ -13,7 +13,7 @@ logger = get_logger(__name__)
 
 class BookQuery(object):
     node = relay.Node.Field()
-    topic = graphene.Field(TopicNode, slug=graphene.String())
+    topic = graphene.Field(TopicOr404Node, slug=graphene.String())
     module = graphene.Field(ModuleNode, slug=graphene.String(), id=graphene.ID())
     chapter = relay.Node.Field(ChapterNode)
     content_block = relay.Node.Field(ContentBlockNode)
@@ -63,5 +63,8 @@ class BookQuery(object):
         if id is not None:
             return get_object(Topic, id)
         if slug is not None:
-            return Topic.objects.get(slug=slug)
+            try:
+                return Topic.objects.get(slug=slug)
+            except Topic.DoesNotExist:
+                return NOT_FOUND
         return None