📝 Add promise documentation

Author: Jeremiah VALERIE

Resources/doc/data-fetching/index.md

@@ -0,0 +1,6 @@
+Data fetching
+=============
+
+* [Promise](promise.md)
+
+Next step [secure your server](../security/index.md).

Resources/doc/data-fetching/promise.md

@@ -0,0 +1,60 @@
+# Promise
+
+The bundle is totally "promise ready", by default it use **Webonyx/GraphQL-Php**
+SyncPromise adapter (supporting the native deferred feature) and it also comes 
+with [ReactPHP/Promise](https://github.com/reactphp/promise) adapter.
+To integrate an other promise implementation, you must create a new service that 
+implements `Overblog\GraphQLBundle\Executor\Promise\PromiseAdapterInterface`.
+
+Config bundle to use the new service:
+
+```yaml
+overblog_graphql:
+    services:
+        promise_adapter: "my.promise_adapter"
+```
+
+You can use the in box `overblog_graphql.react.promise_adapter` service 
+to manage ReactPHP/Promise.
+
+The `overblog_graphql.promise_adapter` service to create promises 
+in resolver like this:
+ 
+```php
+<?php
+
+use Overblog\GraphQLBundle\Executor\Promise\PromiseAdapterInterface;
+
+class MyResolver
+{
+    public function __construct(PromiseAdapterInterface $promiseAdapter)
+    {
+        $this->promiseAdapter = $promiseAdapter;
+    }
+
+    public function resolveQuery()
+    {
+        return $this->promiseAdapter->create(function (callable $resolve) {
+            return $resolve(['name' => 'Luke']);
+        });
+    }
+}
+```
+
+or using native supported promise like this:
+
+```php
+<?php
+
+use React\Promise\Promise as ReactPromise;
+
+class MyResolver
+{
+    public function resolveQuery()
+    {
+        return new ReactPromise(function (callable $resolve) {
+            return $resolve(['name' => 'Luke']);
+        });
+    }
+}
+```

Resources/doc/definitions/index.md

@@ -13,4 +13,4 @@ Go further
 * [Expression language](expression-language.md)
 * [Debug](debug/index.md)
 
-Next step [secure your server](../security/index.md).
+Next step [Data fetching](../data-fetching/index.md).