feat(batch-delegate): added mapping function to createBatchDelegateFn (…

…#1825)

* Added mapping function to createBatchDelegateFn.

This is useful to reverse more complex argsFn processing, as well as more simple cases in which results may not be in identical order as arguments.

Authored-by: Blake Jackson <blakejackson@Blakes-MBP.lan>

packages/batch-delegate/src/createBatchDelegateFn.ts

@@ -9,17 +9,19 @@ import { BatchDelegateOptionsFn, BatchDelegateFn, BatchDelegateOptions } from '.
 export function createBatchDelegateFn<K = any, V = any, C = K>(
   argFn: (args: ReadonlyArray<K>) => Record<string, any>,
   batchDelegateOptionsFn: BatchDelegateOptionsFn,
-  dataLoaderOptions?: DataLoader.Options<K, V, C>
+  dataLoaderOptions?: DataLoader.Options<K, V, C>,
+  resultsFn?: (results: any, keys: ReadonlyArray<K>) => V[]
 ): BatchDelegateFn<K> {
   let cache: WeakMap<ReadonlyArray<FieldNode>, DataLoader<K, V, C>>;
 
   function createBatchFn(options: BatchDelegateOptions) {
     return async (keys: ReadonlyArray<K>) => {
-      const results = await delegateToSchema({
+      let results = await delegateToSchema({
         returnType: new GraphQLList(getNamedType(options.info.returnType) as GraphQLOutputType),
         args: argFn(keys),
         ...batchDelegateOptionsFn(options),
       });
+      results = resultsFn ? resultsFn(results, keys) : results;
       return Array.isArray(results) ? results : keys.map(() => results);
     };
   }