Adds interface to allow for specification of IDs on Apollo Client (#2274

)

* Adds interface to allow for specification of IDs on Apollo Client

The issue came about when trying to specify IDs in Apollo configuration to tell queries about updates when new information becomes available for an Angular project, as per http://dev.apollodata.com/angular2/cache-updates.html

This solution was proposed by @Nyaruiru:
#2201 (comment)

* change id type to string instead of number

* Add Changelog

* fixes changelog

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Change log
 
 ### vNEXT
+- Fix the ability to specify IDs in Apollo configuration to tell queries about updates when new information becomes available [PR #2274](https://github.com/apollographql/apollo-client/pull/2274)
 - Fix response not being included with errors that have response body [PR #2239](https://github.com/apollographql/apollo-client/pull/2239)
 
 - Allow conditional refetchQueries [PR #2234](https://github.com/apollographql/apollo-client/pull/2234)

src/core/types.ts

@@ -33,4 +33,10 @@ export enum FetchType {
   poll = 3,
 }
 
-export type IdGetter = (value: Object) => string | null | undefined;
+export interface IdGetterObj extends Object {
+  __typename?: string;
+  id?: string;
+}
+export declare type IdGetter = (
+  value: IdGetterObj,
+) => string | null | undefined;