Pretend that __typename exists on the root Query.

CHANGELOG.md

@@ -1,5 +1,12 @@
 **Note:** This is a cumulative changelog that outlines all of the Apollo Client project child package changes that were bundled into a specific `apollo-client` release.
 
+## Apollo Client (vNEXT)
+
+### Apollo Cache In-Memory
+
+- Pretend that `__typename` exists on the root Query when matching fragments. <br/>
+  [@benjamn](https://github.com/benjamn) in [#4853](https://github.com/apollographql/apollo-client/pull/4853)
+
 ## Apollo Client (2.6.0)
 
 - In production, `invariant(condition, message)` failures will now include

packages/apollo-cache-inmemory/src/__tests__/fragmentMatcher.ts

@@ -1,6 +1,50 @@
 import { IntrospectionFragmentMatcher } from '../fragmentMatcher';
 import { defaultNormalizedCacheFactory } from '../objectCache';
-import { ReadStoreContext } from '..';
+import { ReadStoreContext } from '../types';
+import { InMemoryCache } from '../inMemoryCache';
+import gql from 'graphql-tag';
+
+describe('FragmentMatcher', () => {
+  it('can match against the root Query', () => {
+    const cache = new InMemoryCache({
+      addTypename: true,
+    });
+
+    const query = gql`
+      query AllPeople {
+        people {
+          id
+          name
+        }
+        ...PeopleTypes
+      }
+      fragment PeopleTypes on Query {
+        __type(name: "Person") {
+          name
+          kind
+        }
+      }
+    `;
+
+    const data = {
+      people: [
+        {
+          __typename: 'Person',
+          id: 123,
+          name: 'Ben',
+        },
+      ],
+      __type: {
+        __typename: '__Type',
+        name: 'Person',
+        kind: 'OBJECT',
+      },
+    };
+
+    cache.writeQuery({ query, data });
+    expect(cache.readQuery({ query })).toEqual(data);
+  });
+});
 
 describe('IntrospectionFragmentMatcher', () => {
   it('will throw an error if match is called if it is not ready', () => {
@@ -42,12 +86,12 @@ describe('IntrospectionFragmentMatcher', () => {
       generated: false,
     };
 
-    const readStoreContext: ReadStoreContext = {
+    const readStoreContext = {
       store,
       returnPartialData: false,
       hasMissingField: false,
-      customResolvers: {},
-    } as any;
+      cacheRedirects: {},
+    } as ReadStoreContext;
 
     expect(ifm.match(idValue as any, 'Item', readStoreContext)).toBe(true);
     expect(ifm.match(idValue as any, 'NotAnItem', readStoreContext)).toBe(

packages/apollo-cache-inmemory/src/fragmentMatcher.ts

@@ -41,13 +41,16 @@ export class HeuristicFragmentMatcher implements FragmentMatcherInterface {
     context: ReadStoreContext,
   ): boolean | 'heuristic' {
     const obj = context.store.get(idValue.id);
+    const isRootQuery = idValue.id === 'ROOT_QUERY';
 
     if (!obj) {
       // https://github.com/apollographql/apollo-client/pull/3507
-      return idValue.id === 'ROOT_QUERY';
+      return isRootQuery;
     }
 
-    if (!obj.__typename) {
+    const { __typename = isRootQuery && 'Query' } = obj;
+
+    if (!__typename) {
       if (shouldWarn()) {
         invariant.warn(`You're using fragments in your queries, but either don't have the addTypename:
   true option set in Apollo Client, or you are trying to write a fragment to the store without the __typename.
@@ -67,7 +70,7 @@ export class HeuristicFragmentMatcher implements FragmentMatcherInterface {
       return 'heuristic';
     }
 
-    if (obj.__typename === typeCondition) {
+    if (__typename === typeCondition) {
       return true;
     }
 
@@ -120,25 +123,28 @@ export class IntrospectionFragmentMatcher implements FragmentMatcherInterface {
     );
 
     const obj = context.store.get(idValue.id);
+    const isRootQuery = idValue.id === 'ROOT_QUERY';
 
     if (!obj) {
       // https://github.com/apollographql/apollo-client/pull/4620
-      return idValue.id === 'ROOT_QUERY';
+      return isRootQuery;
     }
 
+    const { __typename = isRootQuery && 'Query' } = obj;
+
     invariant(
-      obj.__typename,
+      __typename,
       `Cannot match fragment because __typename property is missing: ${JSON.stringify(
         obj,
       )}`,
     );
 
-    if (obj.__typename === typeCondition) {
+    if (__typename === typeCondition) {
       return true;
     }
 
     const implementingTypes = this.possibleTypesMap[typeCondition];
-    if (implementingTypes && implementingTypes.indexOf(obj.__typename) > -1) {
+    if (implementingTypes && implementingTypes.indexOf(__typename) > -1) {
       return true;
     }
 

packages/apollo-cache-inmemory/src/writeToStore.ts

@@ -230,11 +230,12 @@ export class StoreWriter {
           // TODO we need to rewrite the fragment matchers for this to work properly and efficiently
           // Right now we have to pretend that we're passing in an idValue and that there's a store
           // on the context.
-          const idValue = toIdValue({ id: 'self', typename: undefined });
+          const id = dataId || 'self';
+          const idValue = toIdValue({ id, typename: undefined });
           const fakeContext: ReadStoreContext = {
             // NOTE: fakeContext always uses ObjectCache
             // since this is only to ensure the return value of 'matches'
-            store: new ObjectCache({ self: result }),
+            store: new ObjectCache({ [id]: result }),
             cacheRedirects: {},
           };
           const match = context.fragmentMatcherFunction(