Added reverse sort for nullable field

src/Sort.php

@@ -52,6 +52,9 @@ class Sort extends BaseObject
                     $field = substr($field, 1);
                     $sort = 'desc';
                 }
+                if ($this->isStarredNullField($field)) {
+                    $sort = $sort === 'asc' ? 'desc' : 'asc';
+                }
             }
 
             $params[$field] = $sort;
@@ -60,6 +63,11 @@ class Sort extends BaseObject
         return $params;
     }
 
+    private function isStarredNullField($field)
+    {
+        return $field[strlen($field) - 1] === '*';
+    }
+
     public function getOrders()
     {
         $rules = $this->normalizedSortRules();
@@ -67,11 +75,17 @@ class Sort extends BaseObject
 
         $orders = [];
         foreach ($params as $field => $sort) {
-            if (!isset($rules[$field])) {
+            $ruleField = $field;
+            if ($this->isStarredNullField($field)) {
+                $ruleField = substr($field, 0, strlen($field) - 1);
+                $field = '-' . $ruleField;
+            }
+
+            if (! isset($rules[$ruleField])) {
                 continue;
             }
 
-            $sortDef = $rules[$field];
+            $sortDef = $rules[$ruleField];
 
             if ($sortDef && is_callable($sortDef)) {
                 $orders[$field] = $sortDef;

src/capsule/CapsuleCompiler.php

@@ -61,7 +61,11 @@ class CapsuleCompiler implements Compiler
     public function buildSort(array $orders)
     {
         foreach ($orders as $field => $direction) {
-            $this->query->orderBy($field, $direction);
+            if ($field[0] === '-') {
+                $this->query->orderByRaw("$field $direction");
+            } else {
+                $this->query->orderBy($field, $direction);
+            }
         }
     }
 

src/yii2/Yii2Compiler.php

@@ -67,6 +67,9 @@ class Yii2Compiler implements Compiler
         ];
 
         foreach ($orders as $key => $order) {
+            if ($key[0] === '-') {
+                throw new \InvalidArgumentException('Unsupported yet.');
+            }
             $orders[$key] = $orderMap[$order] ?? $order;
         }
 

tests/SortTest.php

@@ -33,7 +33,7 @@ class SortTest extends \PHPUnit_Framework_TestCase
             [
                 '',
                 [],
-            ]
+            ],
         ];
     }
 
@@ -90,7 +90,19 @@ class SortTest extends \PHPUnit_Framework_TestCase
                 [
                     'name' => 'asc',
                     'gender' => 'desc',
-                ]
+                ],
+            ],
+            // reverse null sort
+            [
+                'expired_at*,-gender',
+                [
+                    'expired_at',
+                    'gender',
+                ],
+                [
+                    '-expired_at' => 'desc',
+                    'gender' => 'desc',
+                ],
             ],
         ];
     }