Issue 53: Allow to use treeAttribute as external key

src/NestedSetsBehavior.php

@@ -361,6 +361,8 @@ protected function beforeInsertRootNode()
     {
         if ($this->treeAttribute === false && $this->owner->find()->roots()->exists()) {
             throw new Exception('Can not create more than one root when "treeAttribute" is false.');
+        } elseif ($this->treeAttribute && $this->owner->getAttribute($this->treeAttribute) && $this->owner->find()->roots($this->owner->getAttribute($this->treeAttribute))->exists()) {
+            throw new Exception("Can not create more than one root with {$this->treeAttribute} ".$this->owner->getAttribute($this->treeAttribute));
         }
 
         $this->owner->setAttribute($this->leftAttribute, 1);
@@ -399,7 +401,7 @@ protected function beforeInsertNode($value, $depth)
      */
     public function afterInsert()
     {
-        if ($this->operation === self::OPERATION_MAKE_ROOT && $this->treeAttribute !== false) {
+        if ($this->operation === self::OPERATION_MAKE_ROOT && $this->treeAttribute !== false && !$this->owner->getAttribute($this->treeAttribute)) {
             $this->owner->setAttribute($this->treeAttribute, $this->owner->getPrimaryKey());
             $primaryKey = $this->owner->primaryKey();
 

src/NestedSetsQueryBehavior.php

@@ -21,16 +21,21 @@ class NestedSetsQueryBehavior extends Behavior
 {
     /**
      * Gets the root nodes.
+     * @param mixed $id the optional tree id. Default is `null` to query for all root nodes.
      * @return \yii\db\ActiveQuery the owner
      */
-    public function roots()
+    public function roots($id = null)
     {
         $model = new $this->owner->modelClass();
 
         $this->owner
             ->andWhere([$model->leftAttribute => 1])
             ->addOrderBy([$model->primaryKey()[0] => SORT_ASC]);
 
+        if ($id!==null && $model->treeAttribute!==false) {
+            $this->owner->andWhere([$model->treeAttribute => $id]);
+        }
+
         return $this->owner;
     }
 

tests/NestedSetsBehaviorTest.php

@@ -641,6 +641,29 @@ public function testIsLeaf()
         $this->assertFalse(Tree::findOne(1)->isLeaf());
     }
 
+    public function testMakeTreeWithTreeAttribute()
+    {
+        $dataSet = $this->createFlatXMLDataSet(__DIR__ . '/data/clean.xml');
+        $this->getDatabaseTester()->setDataSet($dataSet);
+        $this->getDatabaseTester()->onSetUp();
+
+        $node = new MultipleTree(['name' => 'Root', 'tree' => 10]);
+        $this->assertTrue($node->makeRoot());
+
+        $dataSet = $this->getConnection()->createDataSet(['multiple_tree']);
+        $expectedDataSet = $this->createFlatXMLDataSet(__DIR__ . '/data/test-make-tree-with-tree-attribute.xml');
+        $this->assertDataSetsEqual($expectedDataSet, $dataSet);
+    }
+
+    /**
+     * @expectedException \yii\db\Exception
+     */
+    public function testMakeRootNewExceptionIsRaisedWhenMultiTreeIsCreatedWithExistingTreeAttribute()
+    {
+        $node = new MultipleTree(['name' => 'Root 4', 'tree' => 1]);
+        $node->makeRoot();
+    }
+
     /**
      * @inheritdoc
      */

tests/data/test-make-tree-with-tree-attribute.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<dataset>
+    <multiple_tree id="1" tree="10" lft="1" rgt="2" depth="0" name="Root"/>
+</dataset>