Take subtypes into account when matching type conditions to extract r…

…epresentations (#804)

The `executeSelectionSet` function in `executeQueryPlan.ts`, which is used to extract field values from a result object to build up representations to send to a subgraph, only looked for exact matches of the `__typename` to the type condition on an inline fragment.

gateway-js/CHANGELOG.md

@@ -4,7 +4,7 @@
 
 > The changes noted within this `vNEXT` section have not been released yet.  New PRs and commits which introduce changes should include an entry in this `vNEXT` section as part of their development.  When a release is being prepared, a new header will be (manually) created below and the appropriate changes within that release will be moved into the new section.
 
--  _Nothing yet! Stay tuned!_
+-  Take subtypes into account when matching type conditions to extract representations. [PR #804](https://github.com/apollographql/federation/pull/804)
 
 ## v0.28.1
 

gateway-js/src/__tests__/executeQueryPlan.test.ts

@@ -1118,4 +1118,64 @@ describe('executeQueryPlan', () => {
       }
     `);
   });
+
+  it(`can execute queries with @include on inline fragment with extension field`, async () => {
+    const operationString = `#graphql
+      query {
+        topProducts(first: 5) {
+          ... on Book @include(if: true) {
+            price
+            inStock
+          }
+          ... on Furniture {
+            price
+            inStock
+          }
+        }
+      }
+    `;
+
+    const operationDocument = gql(operationString);
+
+    const operationContext = buildOperationContext({
+      schema,
+      operationDocument,
+    });
+
+    const queryPlan = queryPlanner.buildQueryPlan(operationContext);
+
+    const response = await executeQueryPlan(
+      queryPlan,
+      serviceMap,
+      buildRequestContext(),
+      operationContext,
+    );
+
+    expect(response.data).toMatchInlineSnapshot(`
+      Object {
+        "topProducts": Array [
+          Object {
+            "inStock": true,
+            "price": "899",
+          },
+          Object {
+            "inStock": false,
+            "price": "1299",
+          },
+          Object {
+            "inStock": true,
+            "price": "54",
+          },
+          Object {
+            "inStock": true,
+            "price": "39",
+          },
+          Object {
+            "inStock": false,
+            "price": "29",
+          },
+        ],
+      }
+    `);
+  });
 });

gateway-js/src/executeQueryPlan.ts

@@ -10,6 +10,8 @@ import {
   TypeNameMetaFieldDef,
   GraphQLFieldResolver,
   GraphQLFormattedError,
+  isAbstractType,
+  GraphQLSchema,
 } from 'graphql';
 import { Trace, google } from 'apollo-reporting-protobuf';
 import { defaultRootOperationNameLookup } from '@apollo/federation';
@@ -247,7 +249,11 @@ async function executeFetch<TContext>(
     const representationToEntity: number[] = [];
 
     entities.forEach((entity, index) => {
-      const representation = executeSelectionSet(entity, requires);
+      const representation = executeSelectionSet(
+        context.operationContext,
+        entity,
+        requires,
+      );
       if (representation && representation[TypeNameMetaFieldDef.name]) {
         representations.push(representation);
         representationToEntity.push(index);
@@ -401,6 +407,7 @@ async function executeFetch<TContext>(
  * @param selectionSet
  */
 function executeSelectionSet(
+  operationContext: OperationContext,
   source: Record<string, any> | null,
   selections: QueryPlanSelectionNode[],
 ): Record<string, any> | null {
@@ -424,10 +431,13 @@ function executeSelectionSet(
         }
         if (Array.isArray(source[responseName])) {
           result[responseName] = source[responseName].map((value: any) =>
-            selections ? executeSelectionSet(value, selections) : value,
+            selections
+              ? executeSelectionSet(operationContext, value, selections)
+              : value,
           );
         } else if (selections) {
           result[responseName] = executeSelectionSet(
+            operationContext,
             source[responseName],
             selections,
           );
@@ -441,10 +451,10 @@ function executeSelectionSet(
         const typename = source && source['__typename'];
         if (!typename) continue;
 
-        if (typename === selection.typeCondition) {
+        if (doesTypeConditionMatch(operationContext.schema, selection.typeCondition, typename)) {
           deepMerge(
             result,
-            executeSelectionSet(source, selection.selections),
+            executeSelectionSet(operationContext, source, selection.selections),
           );
         }
         break;
@@ -454,6 +464,32 @@ function executeSelectionSet(
   return result;
 }
 
+function doesTypeConditionMatch(
+  schema: GraphQLSchema,
+  typeCondition: string,
+  typename: string,
+): boolean {
+  if (typeCondition === typename) {
+    return true;
+  }
+
+  const type = schema.getType(typename);
+  if (!type) {
+    return false;
+  }
+
+  const conditionalType = schema.getType(typeCondition);
+  if (!conditionalType) {
+    return false;
+  }
+
+  if (isAbstractType(conditionalType)) {
+    return schema.isSubType(conditionalType, type);
+  }
+
+  return false;
+}
+
 function flattenResultsAtPath(value: any, path: ResponsePath): any {
   if (path.length === 0) return value;
   if (value === undefined || value === null) return value;