Add imperative read method to ApolloClient

CHANGELOG.md

@@ -3,7 +3,7 @@
 Expect active development and potentially significant breaking changes in the `0.x` track. We'll try to be diligent about releasing a `1.0` version in a timely fashion (ideally within 3 to 6 months), to signal the start of a more stable API.
 
 ### vNEXT
-- ...
+- Add imperative `read` method to client for arbitrary data access from the store. [PR #1280](https://github.com/apollographql/apollo-client/pull/1280)
 
 ### 0.8.6
 - Fix bug that caused `refetch` to not refetch in some cases [PR #1264](https://github.com/apollographql/apollo-client/pull/1264)

src/ApolloClient.ts

@@ -11,6 +11,8 @@ import {
   SelectionSetNode,
   /* tslint:enable */
 
+  DocumentNode,
+  FragmentDefinitionNode,
 } from 'graphql';
 
 import {
@@ -58,6 +60,10 @@ import {
   storeKeyNameFromFieldNameAndArgs,
 } from './data/storeUtils';
 
+import {
+  readQueryFromStore,
+} from './data/readFromStore';
+
 import {
   version,
 } from './version';
@@ -336,6 +342,101 @@ export default class ApolloClient {
     return this.queryManager.startGraphQLSubscription(realOptions);
   }
 
+  /**
+   * Tries to read some data from the store without making a network request.
+   * This method will start at the root query. To start at a a specific id in
+   * the store then use `readFragment`.
+   */
+  public readQuery <QueryType>({
+    query,
+    variables,
+    returnPartialData,
+  }: {
+    query: DocumentNode,
+    variables?: Object,
+    returnPartialData?: boolean,
+  }): QueryType {
+    this.initStore();
+
+    const reduxRootSelector = this.reduxRootSelector || defaultReduxRootSelector;
+
+    return readQueryFromStore<QueryType>({
+      store: reduxRootSelector(this.store.getState()).data,
+      query,
+      variables,
+      returnPartialData,
+    });
+  }
+
+  /**
+   * Tries to read some data from the store without making a network request.
+   * This method will read a GraphQL fragment from any arbitrary id in the
+   * store. Unlike `readQuery` which will only read from the root query.
+   */
+  public readFragment <FragmentType>({
+    id,
+    fragment,
+    fragmentName,
+    variables,
+    returnPartialData,
+  }: {
+    id: string,
+    fragment: DocumentNode,
+    fragmentName?: string,
+    variables?: Object,
+    returnPartialData?: boolean,
+  }): FragmentType {
+    this.initStore();
+
+    const reduxRootSelector = this.reduxRootSelector || defaultReduxRootSelector;
+    let actualFragmentName = fragmentName;
+
+    // If the user did not give us a fragment name then let us try to get a
+    // name from a single fragment in the definition.
+    if (typeof actualFragmentName === 'undefined') {
+      const fragments = fragment.definitions.filter(({ kind }) => kind === 'FragmentDefinition') as Array<FragmentDefinitionNode>;
+      if (fragments.length !== 1) {
+        throw new Error(`Found ${fragments.length} fragments when exactly 1 was expected because \`fragmentName\` was not provided.`);
+      }
+      actualFragmentName = fragments[0].name.value;
+    }
+
+    // Generate a query document with an operation that simply spreads the
+    // fragment inside of it. This is necessary to be compatible with our
+    // current store implementation, but we want users to write fragments to
+    // support GraphQL tooling everywhere.
+    const query: DocumentNode = {
+      ...fragment,
+      definitions: [
+        {
+          kind: 'OperationDefinition',
+          operation: 'query',
+          selectionSet: {
+            kind: 'SelectionSet',
+            selections: [
+              {
+                kind: 'FragmentSpread',
+                name: {
+                  kind: 'Name',
+                  value: actualFragmentName,
+                },
+              },
+            ],
+          },
+        },
+        ...fragment.definitions,
+      ],
+    };
+
+    return readQueryFromStore<FragmentType>({
+      rootId: id,
+      store: reduxRootSelector(this.store.getState()).data,
+      query,
+      variables,
+      returnPartialData,
+    });
+  }
+
   /**
    * Returns a reducer function configured according to the `reducerConfig` instance variable.
    */

src/data/readFromStore.ts

@@ -56,6 +56,7 @@ export type ReadQueryOptions = {
   variables?: Object,
   returnPartialData?: boolean,
   previousResult?: any,
+  rootId?: string,
   config?: ApolloReducerConfig,
 };
 
@@ -247,6 +248,7 @@ export function diffQueryAgainstStore({
   variables,
   returnPartialData = true,
   previousResult,
+  rootId = 'ROOT_QUERY',
   config,
 }: ReadQueryOptions): DiffResult {
   // Throw the right validation error by trying to find a query in the document
@@ -264,7 +266,7 @@ export function diffQueryAgainstStore({
 
   const rootIdValue = {
     type: 'id',
-    id: 'ROOT_QUERY',
+    id: rootId,
     previousResult,
   };