Started to implement moving a subtree as a root

src/Model/Behavior/TreeBehavior.php

@@ -91,13 +91,17 @@ public function beforeSave(Event $event, Entity $entity) {
 
 		if ($isNew && !$parent) {
 			$edge = $this->_getMax();
-			$entity->set($config['left'],$edge + 1);
+			$entity->set($config['left'], $edge + 1);
 			$entity->set($config['right'], $edge + 2);
 		}
 
 		if (!$isNew && $dirty && $parent) {
 			$this->_setParent($entity, $parent);
 		}
+
+		if (!$isNew && $dirty && !$parent) {
+			$this->_setAsRoot($entity);
+		}
 	}
 
 	protected function _getParent($id) {
@@ -161,6 +165,19 @@ protected function _setParent($entity, $parent) {
 		$entity->set($config['right'], $targetRight);
 	}
 
+	protected function _setAsRoot($entity) {
+		$config = $this->config();
+		$edge = $this->_getMax();
+		$right = $entity->get($config['right']);
+		$left = $entity->get($config['left']);
+		$internalLeft = $left + 1;
+		$internalRight = $right - 1;
+
+		$entity->set($config['left'], $edge + 1);
+		$entity->set($config['right'], $edge + $right - 1);
+		$this->_sync($edge - 1, '+', "BETWEEN {$internalLeft} AND {$internalRight}");
+	}
+
 	public function findPath($query, $options) {
 		if (empty($options['for'])) {
 			throw new \InvalidArgumentException("The 'for' key is required for find('path')");

tests/TestCase/Model/Behavior/TreeBehaviorTest.php

@@ -460,4 +460,24 @@ public function testReParentLeafRight() {
 		$this->assertEquals(range(1, 22), $numbers);
 	}
 
+/**
+ * Tests moving as a new root
+ *
+ * @return void
+ */
+	public function testRootingSubTree() {
+		$table = TableRegistry::get('NumberTrees');
+		$table->addBehavior('Tree');
+		$entity = $table->get(2);
+		$entity->parent_id = null;
+		$this->assertSame($entity, $table->save($entity));
+		$this->assertEquals(23, $entity->lft);
+		$this->assertEquals(30, $entity->rght);
+
+		$result = $table->find()->order('lft')->hydrate(false)->toArray();
+		$table->recover();
+		$expected = $table->find()->order('lft')->hydrate(false)->toArray();
+		$this->assertEquals($expected, $result);
+	}
+
 }