add move by

README.md

@@ -171,6 +171,13 @@ $myModel->moveOrderDown();
 $myModel->moveOrderUp();
 ```
 
+Or you can move model up or down by specific amount:
+
+```php
+$myModel->moveDownBy(6);
+$myModel->moveUpBy(4);
+```
+
 You can also move a model to the first or last position:
 
 ```php

src/SortableTrait.php

@@ -151,6 +151,68 @@ public function moveToStart(): static
         return $this;
     }
 
+    public function moveDownBy(int $amount): static
+    {
+        if ($amount < 1) {
+            return $this;
+        }
+
+        if ($amount === 1) {
+            return $this->moveOrderDown();
+        }
+
+        $orderColumnName = $this->determineOrderColumnName();
+
+        $newOrder = (int) $this->buildSortQuery()
+            ->where($orderColumnName, '<=', $this->$orderColumnName + $amount)
+            ->max($orderColumnName);
+
+        if ($this->$orderColumnName === $newOrder) {
+            return $this;
+        }
+
+        $oldOrder = $this->$orderColumnName;
+        $this->$orderColumnName = $newOrder;
+        $this->save();
+
+        $this->buildSortQuery()->where($this->getKeyName(), '!=', $this->getKey())
+            ->whereBetween($orderColumnName, [$oldOrder, $newOrder])
+            ->decrement($orderColumnName);
+
+        return $this;
+    }
+
+    public function moveUpBy(int $amount): static
+    {
+        if ($amount < 1) {
+            return $this;
+        }
+
+        if ($amount === 1) {
+            return $this->moveOrderUp();
+        }
+
+        $orderColumnName = $this->determineOrderColumnName();
+
+        $newOrder = (int) $this->buildSortQuery()
+            ->where($orderColumnName, '>=', $this->$orderColumnName - $amount)
+            ->min($orderColumnName);
+
+        if ($this->$orderColumnName === $newOrder) {
+            return $this;
+        }
+
+        $oldOrder = $this->$orderColumnName;
+        $this->$orderColumnName = $newOrder;
+        $this->save();
+
+        $this->buildSortQuery()->where($this->getKeyName(), '!=', $this->getKey())
+            ->whereBetween($orderColumnName, [$newOrder, $oldOrder])
+            ->increment($orderColumnName);
+
+        return $this;
+    }
+
     public function moveToEnd(): static
     {
         $maxOrder = $this->getHighestOrderNumber();

tests/SortableTest.php

@@ -371,4 +371,52 @@ public function it_can_tell_if_element_is_last_in_order()
         $this->assertTrue($model[$model->count() - 1]->isLastInOrder());
         $this->assertFalse($model[$model->count() - 2]->isLastInOrder());
     }
+
+    /** @test */
+    public function it_can_move_order_down_by_amount()
+    {
+        $moveBy = 6;
+        $oldOrder = 4;
+
+        $model = Dummy::find($oldOrder);
+        $others = Dummy::whereBetween('order_column', [$oldOrder + 1, $oldOrder + $moveBy])->get();
+
+        $this->assertEquals($model->order_column, $oldOrder);
+        foreach ($others as $index => $other) {
+            $this->assertEquals($other->order_column, $oldOrder + $index + 1);
+        }
+
+        $this->assertNotFalse($model->moveDownBy($moveBy));
+
+        $others = Dummy::whereKey($others)->get();
+
+        $this->assertEquals($model->order_column, $oldOrder + $moveBy);
+        foreach ($others as $index => $other) {
+            $this->assertEquals($other->order_column, $oldOrder + $index);
+        }
+    }
+
+    /** @test */
+    public function it_can_move_order_up_by_amount()
+    {
+        $moveBy = 6;
+        $oldOrder = 14;
+
+        $model = Dummy::find($oldOrder);
+        $others = Dummy::whereBetween('order_column', [$oldOrder - $moveBy, $oldOrder - 1])->ordered('desc')->get();
+
+        $this->assertEquals($model->order_column, $oldOrder);
+        foreach ($others as $index => $other) {
+            $this->assertEquals($other->order_column, $oldOrder - $index - 1);
+        }
+
+        $this->assertNotFalse($model->moveUpBy($moveBy));
+
+        $others = Dummy::whereKey($others)->ordered('desc')->get();
+
+        $this->assertEquals($model->order_column, $oldOrder - $moveBy);
+        foreach ($others as $index => $other) {
+            $this->assertEquals($other->order_column, $oldOrder - $index);
+        }
+    }
 }