Update doc from new PR

Author: vincentchalamon

core/default-order.md

@@ -1,4 +1,4 @@
-# Override default order
+# Override Default Order
 
 API Platform Core provides an easy way to override default order in your collection.
 
@@ -11,26 +11,77 @@ By default, it will order by resource identifier(s) using ASC direction. If you
 
 namespace AppBundle\Entity;
 
-use ApiPlatform\Core\Annotation\ApiProperty;
 use ApiPlatform\Core\Annotation\ApiResource;
 
 /**
- * @ApiResource(attributes={"order"={"foo", "ASC"}})
+ * @ApiResource(attributes={"order"={"foo": "ASC"}})
  */
 class Book
 {
     // ...
 
     /**
      * ...
-     * @ApiProperty()
      */
     public $foo;
 }
 ```
 
-This `order` attribute is used as an array with 2 entries: the first one defines the order field, the second one defined the direction.
-If you only specify the first one, `ASC` direction will be used as default.
+This `order` attribute is used as an array: the key defines the order field, the values defines the direction.
+If you only specify the key, `ASC` direction will be used as default. For example, to order by `foo` & `bar`:
+
+```php
+<?php
+
+// src/AppBundle/Entity/Book.php
+
+namespace AppBundle\Entity;
+
+use ApiPlatform\Core\Annotation\ApiResource;
+
+/**
+ * @ApiResource(attributes={"order"={"foo", "bar"}})
+ */
+class Book
+{
+    // ...
+
+    /**
+     * ...
+     */
+    public $foo;
+
+    /**
+     * ...
+     */
+    public $bar;
+}
+```
+
+It's also possible to configure the default filter on an association property:
+
+```php
+<?php
+
+// src/AppBundle/Entity/Book.php
+
+namespace AppBundle\Entity;
+
+use ApiPlatform\Core\Annotation\ApiResource;
+
+/**
+ * @ApiResource(attributes={"order"={"author.username"}})
+ */
+class Book
+{
+    // ...
+
+    /**
+     * @var User
+     */
+    public $author;
+}
+```
 
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