Read from cache again in ObservableQuery#getCurrentResult.

This partially reverts two commits from PR #5565, preserving related
improvements that have happened in the meantime:

* Revert "Remove partial field from ApolloCurrentQueryResult type."
  This reverts commit ca2cef6.

* Revert "Stop reading from cache in ObservableQuery#getCurrentResult."
  This reverts commit 01376a3.

One of the motivations behind the original changes was to lay the
foundations for eventually supporting asynchronous (Promise-based) cache
reads, but that form of asynchrony is no longer a goal of Apollo Client
3.0 or any planned future version, so there's not as much benefit to
weakening getCurrentResult in this way.

On the other hand, allowing getCurrentResult to read synchronously from
the cache ensures that custom field read functions can return new results
immediately, which helps with issues like #5782.

Immediate cache reads have also been the behavior of Apollo Client for
much longer than #5565, which makes this change appealing from an
ease-of-upgrading perspective.

src/core/ObservableQuery.ts

@@ -20,6 +20,7 @@ import { isNonEmptyArray } from '../utilities/common/arrays';
 
 export type ApolloCurrentQueryResult<T> = ApolloQueryResult<T> & {
   error?: ApolloError;
+  partial?: boolean;
 };
 
 export interface FetchMoreOptions<
@@ -130,9 +131,18 @@ export class ObservableQuery<
     });
   }
 
+  /**
+   * Return the result of the query from the local cache as well as some fetching status
+   * `loading` and `networkStatus` allow to know if a request is in flight
+   * `partial` lets you know if the result from the local cache is complete or partial
+   */
   public getCurrentResult(): ApolloCurrentQueryResult<TData> {
-    const { lastResult, lastError } = this;
-    const { fetchPolicy } = this.options;
+    const {
+      lastResult,
+      lastError,
+      options: { fetchPolicy },
+    } = this;
+
     const isNetworkFetchPolicy =
       fetchPolicy === 'network-only' ||
       fetchPolicy === 'no-cache';
@@ -155,6 +165,9 @@ export class ObservableQuery<
       return result;
     }
 
+    const { data, partial } = this.queryManager.getCurrentQueryResult(this);
+    Object.assign(result, { data, partial });
+
     const queryStoreValue = this.queryManager.queryStore.get(this.queryId);
     if (queryStoreValue) {
       const { networkStatus } = queryStoreValue;
@@ -191,9 +204,27 @@ export class ObservableQuery<
       if (queryStoreValue.graphQLErrors && this.options.errorPolicy === 'all') {
         result.errors = queryStoreValue.graphQLErrors;
       }
+
+    } else {
+      // We need to be careful about the loading state we show to the user, to try
+      // and be vaguely in line with what the user would have seen from .subscribe()
+      // but to still provide useful information synchronously when the query
+      // will not end up hitting the server.
+      // See more: https://github.com/apollographql/apollo-client/issues/707
+      // Basically: is there a query in flight right now?
+      const loading = isNetworkFetchPolicy ||
+        (partial && fetchPolicy !== 'cache-only');
+
+      Object.assign(result, {
+        loading,
+        networkStatus: loading ? NetworkStatus.loading : NetworkStatus.ready,
+      });
     }
 
-    this.updateLastResult(result);
+    if (!partial) {
+      result.stale = false;
+      this.updateLastResult(result);
+    }
 
     return result;
   }

src/core/QueryManager.ts

@@ -1052,7 +1052,7 @@ export class QueryManager<TStore> {
     this.queries.delete(queryId);
   }
 
-  private getCurrentQueryResult<T>(
+  public getCurrentQueryResult<T>(
     observableQuery: ObservableQuery<T>,
     optimistic: boolean = true,
   ): {

src/core/__tests__/ObservableQuery.ts

@@ -1450,6 +1450,7 @@ describe('ObservableQuery', () => {
           loading: false,
           networkStatus: 7,
           stale: false,
+          partial: false,
         });
         resolve();
       });
@@ -1459,6 +1460,7 @@ describe('ObservableQuery', () => {
         data: undefined,
         networkStatus: 1,
         stale: false,
+        partial: true,
       });
 
       setTimeout(
@@ -1468,12 +1470,40 @@ describe('ObservableQuery', () => {
             data: undefined,
             networkStatus: 1,
             stale: false,
+            partial: true,
           });
         }),
         0,
       );
     });
 
+    itAsync('returns results from the store immediately', (resolve, reject) => {
+      const queryManager = mockQueryManager(reject, {
+        request: { query, variables },
+        result: { data: dataOne },
+      });
+
+      return queryManager.query({ query, variables }).then((result: any) => {
+        expect(stripSymbols(result)).toEqual({
+          data: dataOne,
+          loading: false,
+          networkStatus: 7,
+          stale: false,
+        });
+        const observable = queryManager.watchQuery({
+          query,
+          variables,
+        });
+        expect(stripSymbols(observable.getCurrentResult())).toEqual({
+          data: dataOne,
+          loading: true,
+          networkStatus: NetworkStatus.loading,
+          stale: false,
+          partial: false,
+        });
+      }).then(resolve, reject);
+    });
+
     itAsync('returns errors from the store immediately', (resolve, reject) => {
       const queryManager = mockQueryManager(reject, {
         request: { query, variables },
@@ -1563,7 +1593,7 @@ describe('ObservableQuery', () => {
       }).then(resolve, reject);
     });
 
-    itAsync('returns partial data from the store', (resolve, reject) => {
+    itAsync('returns partial data from the store immediately', (resolve, reject) => {
       const superQuery = gql`
         query superQuery($id: ID!) {
           people_one(id: $id) {
@@ -1600,10 +1630,11 @@ describe('ObservableQuery', () => {
         });
 
         expect(observable.getCurrentResult()).toEqual({
-          data: void 0,
+          data: dataOne,
           loading: true,
           networkStatus: 1,
           stale: false,
+          partial: true,
         });
 
         // we can use this to trigger the query
@@ -1618,28 +1649,19 @@ describe('ObservableQuery', () => {
 
           if (handleCount === 1) {
             expect(subResult).toEqual({
-              data: void 0,
+              data: dataOne,
               loading: true,
               networkStatus: 1,
               stale: false,
             });
 
           } else if (handleCount === 2) {
-            expect(subResult).toEqual({
-              data: dataOne,
-              loading: false,
-              networkStatus: 7,
-              stale: false,
-            });
-
-          } else if (handleCount === 3) {
             expect(subResult).toEqual({
               data: superDataOne,
               loading: false,
               networkStatus: 7,
               stale: false,
             });
-
             resolve();
           }
         });
@@ -1670,6 +1692,7 @@ describe('ObservableQuery', () => {
           loading: true,
           networkStatus: 1,
           stale: false,
+          partial: false,
         });
 
         subscribeAndCount(reject, observable, (handleCount, subResult) => {
@@ -1678,30 +1701,20 @@ describe('ObservableQuery', () => {
             loading,
             networkStatus,
           } = observable.getCurrentResult();
-
           expect(subResult).toEqual({
             data,
             loading,
             networkStatus,
             stale: false,
           });
 
-          if (handleCount === 1) {
-            expect(stripSymbols(subResult)).toEqual({
-              data: void 0,
-              loading: true,
-              networkStatus: NetworkStatus.loading,
-              stale: false,
-            });
-
-          } else if (handleCount === 2) {
+          if (handleCount === 2) {
             expect(stripSymbols(subResult)).toEqual({
               data: dataTwo,
               loading: false,
-              networkStatus: NetworkStatus.ready,
+              networkStatus: 7,
               stale: false,
             });
-
             resolve();
           }
         });
@@ -1727,12 +1740,12 @@ describe('ObservableQuery', () => {
           variables,
           fetchPolicy: 'no-cache',
         });
-
         expect(stripSymbols(observable.getCurrentResult())).toEqual({
           data: undefined,
           loading: true,
           networkStatus: 1,
           stale: false,
+          partial: false,
         });
 
         subscribeAndCount(reject, observable, (handleCount, subResult) => {
@@ -1748,6 +1761,7 @@ describe('ObservableQuery', () => {
               loading,
               networkStatus,
               stale: false,
+              partial: false,
             });
           } else if (handleCount === 2) {
             expect(stripSymbols(subResult)).toEqual({

src/react/data/QueryData.ts

@@ -353,7 +353,7 @@ export class QueryData<TData, TVariables> extends OperationData {
     } else {
       // Fetch the current result (if any) from the store.
       const currentResult = this.currentObservable.query!.getCurrentResult();
-      const { loading, networkStatus, errors } = currentResult;
+      const { loading, partial, networkStatus, errors } = currentResult;
       let { error, data } = currentResult;
 
       // Until a set naming convention for networkError and graphQLErrors is
@@ -390,6 +390,7 @@ export class QueryData<TData, TVariables> extends OperationData {
         const { partialRefetch } = options;
         if (
           partialRefetch &&
+          partial &&
           (!data || Object.keys(data).length === 0) &&
           fetchPolicy !== 'cache-only'
         ) {