Support positional and keyed batch results

README.md

@@ -71,10 +71,13 @@ minimal outgoing data requests.
 #### Batch Function
 
 A batch loading function accepts an Array of keys, and returns a Promise which
-resolves to an Array of values. There are a few constraints that must be upheld:
+resolves to values in one of these forms:
 
- * The Array of values must be the same length as the Array of keys.
- * Each index in the Array of values must correspond to the same index in the Array of keys.
+ * A list with the same length and order as the Array of keys.
+ * A keyed Array or `ArrayAccess` value. Missing keys resolve to `null`.
+
+Object keys require positional list results or an `ArrayAccess` result that
+supports those keys.
 
 For example, if your batch function was provided the Array of keys: `[ 2, 9, 6, 1 ]`,
 and loading from a back-end service returned the values:

lib/promise-adapter/src/Adapter/WebonyxGraphQLSyncPromiseAdapter.php

@@ -32,7 +32,7 @@ class WebonyxGraphQLSyncPromiseAdapter implements PromiseAdapterInterface
 
     public function __construct(?SyncPromiseAdapter $webonyxPromiseAdapter = null)
     {
-        $webonyxPromiseAdapter = $webonyxPromiseAdapter?:new SyncPromiseAdapter();
+        $webonyxPromiseAdapter = $webonyxPromiseAdapter?:new \Overblog\DataLoader\Promise\Adapter\Webonyx\GraphQL\SyncPromiseAdapter();
         $this->setWebonyxPromiseAdapter($webonyxPromiseAdapter);
     }
 

src/DataLoader.php

@@ -417,39 +417,61 @@ private function dispatchQueueBatch(array $queue)
 
         // Await the resolution of the call to batchLoadFn.
         $batchPromise->then(
-            function ($values) use ($keys, $queue) {
-                // Assert the expected resolution from batchLoadFn.
-                if (!is_array($values) && !$values instanceof \Traversable) {
-                    throw new \RuntimeException(
-                        'DataLoader must be constructed with a function which accepts ' .
-                        'Array<key> and returns Promise<Array<value>>, but the function did ' .
-                        sprintf('not return a Promise of an Array: %s.', gettype($values))
-                    );
-                }
-                if (count($values) !== count($keys)) {
-                    throw new \RuntimeException(
-                        'DataLoader must be constructed with a function which accepts ' .
-                        'Array<key> and returns Promise<Array<value>>, but the function did ' .
-                        'not return a Promise of an Array of the same length as the Array of keys.'
-                    );
-                }
-
-                // Step through the values, resolving or rejecting each Promise in the
-                // loaded queue.
-                foreach ($queue as $index => $data) {
-                    $value = $values[$index];
-                    if ($value instanceof \Throwable) {
-                        $data['reject']($value);
-                    } else {
-                        $data['resolve']($value);
-                    }
-                };
+            function ($values) use ($queue) {
+                $this->resolveDispatchedBatch($values, $queue);
             }
         )->then(null, function ($error) use ($queue) {
             $this->failedDispatch($queue, $error);
         });
     }
 
+    /**
+     * Fan a resolved batch result out to the individual queued promises.
+     *
+     * @param mixed $values
+     * @param array $queue
+     */
+    private function resolveDispatchedBatch($values, $queue)
+    {
+        // Assert the expected resolution from batchLoadFn.
+        if (!is_array($values) && !$values instanceof \Traversable) {
+            throw new \RuntimeException(
+                'DataLoader must be constructed with a function which accepts ' .
+                'Array<key> and returns Promise<Array<value>>, but the function did ' .
+                sprintf('not return a Promise of an Array: %s.', gettype($values))
+            );
+        }
+
+        if ($values instanceof \Traversable && !$values instanceof \ArrayAccess) {
+            $values = iterator_to_array($values);
+        }
+
+        // Step through the values, resolving or rejecting each Promise in the
+        // loaded queue.
+        foreach ($queue as $index => $data) {
+            $key = $data['key'];
+            if (is_array($values)) {
+                if (array_is_list($values)) {
+                    $value = $values[$index] ?? null;
+                } elseif (is_int($key) || is_string($key) || is_float($key) || is_bool($key)) {
+                    $value = $values[$key] ?? null;
+                } else {
+                    $value = null;
+                }
+            } elseif ($values instanceof \ArrayAccess) {
+                $value = $values->offsetExists($key) ? $values->offsetGet($key) : null;
+            } else {
+                $value = null;
+            }
+
+            if ($value instanceof \Throwable) {
+                $data['reject']($value);
+            } else {
+                $data['resolve']($value);
+            }
+        }
+    }
+
     /**
      * Do not cache individual loads if the entire batch dispatch fails,
      * but still reject each request so they do not hang.

tests/AbuseTestCase.php

@@ -84,14 +84,13 @@ public function testBatchFunctionMustReturnAPromiseOfAnArrayNotNull()
     /**
      * @group provides-descriptive-error-messages-for-api-abuse
      */
-    public function testBatchFunctionMustPromiseAnArrayOfCorrectLength()
+    public function testBatchFunctionMayReturnMissingValues()
     {
-        $this->expectException(RuntimeException::class);
-        $this->expectExceptionMessage('DataLoader must be constructed with a function which accepts Array<key> and returns Promise<Array<value>>, but the function did not return a Promise of an Array of the same length as the Array of keys.');
-
-        DataLoader::await(self::idLoader(function () {
+        $value = DataLoader::await(self::idLoader(function () {
             return self::$promiseAdapter->createFulfilled([]);
         })->load(1));
+
+        $this->assertNull($value);
     }
 
     /**

tests/DataLoadTestCase.php

@@ -51,6 +51,24 @@ public function testSupportsLoadingMultipleKeysInOneCall()
         $this->assertEquals([], DataLoader::await($promiseEmpty));
     }
 
+    /**
+     * @group accepts-any-kind-of-key
+     */
+    public function testSupportsKeyedResultsWithMissingValues()
+    {
+        $loader = new DataLoader(function () {
+            return self::$promiseAdapter->createFulfilled(['present' => 'value']);
+        }, self::$promiseAdapter);
+
+        list($present, $missing) = DataLoader::await(self::$promiseAdapter->createAll([
+            $loader->load('present'),
+            $loader->load('missing'),
+        ]));
+
+        $this->assertEquals('value', $present);
+        $this->assertNull($missing);
+    }
+
     /**
      * @group primary-api
      */