Added Collection::listNested()

src/Collection/CollectionTrait.php

@@ -21,8 +21,10 @@
 use Cake\Collection\Iterator\FilterIterator;
 use Cake\Collection\Iterator\InsertIterator;
 use Cake\Collection\Iterator\MapReduce;
+use Cake\Collection\Iterator\NestIterator;
 use Cake\Collection\Iterator\ReplaceIterator;
 use Cake\Collection\Iterator\SortIterator;
+use Cake\Collection\Iterator\TreeIterator;
 use LimitIterator;
 
 /**
@@ -857,4 +859,16 @@ public function compile($preserveKeys = true) {
 		return new Collection($this->toArray($preserveKeys));
 	}
 
+/**
+ * 
+ *
+ * @return void
+ */
+	public function listNested($nestingKey = 'children') {
+		return new TreeIterator(
+			new NestIterator($this, $nestingKey),
+			TreeIterator::SELF_FIRST
+		);
+	}
+
 }

src/Collection/Iterator/NestIterator.php

@@ -0,0 +1,48 @@
+<?php
+/**
+ * CakePHP(tm) : Rapid Development Framework (http://cakephp.org)
+ * Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ *
+ * Licensed under The MIT License
+ * For full copyright and license information, please see the LICENSE.txt
+ * Redistributions of files must retain the above copyright notice.
+ *
+ * @copyright     Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ * @link          http://cakephp.org CakePHP(tm) Project
+ * @since         3.0.0
+ * @license       MIT License (http://www.opensource.org/licenses/mit-license.php)
+ */
+namespace Cake\Collection\Iterator;
+
+use Cake\Collection\Collection;
+use RecursiveIterator;
+
+class NestIterator extends Collection implements RecursiveIterator{
+
+	protected $_nestKey;
+
+	public function __construct($items, $nestKey) {
+		parent::__construct($items);
+		$this->_nestKey = $nestKey;
+	}
+
+	public function getChildren() {
+		$property = $this->_propertyExtractor($this->_nestKey);
+		return new self($property($this->current()), $this->_nestKey);
+	}
+
+	public function hasChildren () {
+		$property = $this->_propertyExtractor($this->_nestKey);
+		$children = $property($this->current());
+
+		if (is_array($children)) {
+			return !empty($children);
+		}
+
+		if ($children instanceof \Traversable) {
+			return true;
+		}
+
+		return false;
+	}
+}

src/Collection/Iterator/TreeIterator.php

@@ -0,0 +1,24 @@
+<?php
+/**
+ * CakePHP(tm) : Rapid Development Framework (http://cakephp.org)
+ * Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ *
+ * Licensed under The MIT License
+ * For full copyright and license information, please see the LICENSE.txt
+ * Redistributions of files must retain the above copyright notice.
+ *
+ * @copyright     Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ * @link          http://cakephp.org CakePHP(tm) Project
+ * @since         3.0.0
+ * @license       MIT License (http://www.opensource.org/licenses/mit-license.php)
+ */
+namespace Cake\Collection\Iterator;
+
+use Cake\Collection\CollectionTrait;
+use RecursiveIteratorIterator;
+
+class TreeIterator extends RecursiveIteratorIterator {
+
+	use CollectionTrait;
+
+}

tests/TestCase/Collection/CollectionTest.php

@@ -872,4 +872,43 @@ public function testInsert() {
 		);
 	}
 
+/**
+ * Tests the listNested method with the default 'children' nesting key
+ *
+ * @return void
+ */
+	public function testListNested() {
+		$items = [
+			['id' => 1, 'parent_id' => null],
+			['id' => 2, 'parent_id' => 1],
+			['id' => 3, 'parent_id' => 2],
+			['id' => 4, 'parent_id' => 2],
+			['id' => 5, 'parent_id' => 3],
+			['id' => 6, 'parent_id' => null],
+			['id' => 7, 'parent_id' => 3],
+			['id' => 8, 'parent_id' => 4],
+			['id' => 9, 'parent_id' => 6],
+			['id' => 10, 'parent_id' => 6]
+		];
+		$collection = (new Collection($items))->nest('id', 'parent_id')->listNested();
+		$this->assertEquals(
+			[1, 2, 3, 5, 7, 4, 8, 6, 9, 10],
+			$collection->extract('id')->toArray(false)
+		);
+	}
+
+/**
+ * Tests using listNested with a different nesting key
+ *
+ * @return void
+ */
+	public function testListNestedCustomKey() {
+		$items = [
+			['id' => 1, 'stuff' => [['id' => 2, 'stuff' => [['id' => 3]]]]],
+			['id' => 4, 'stuff' => [['id' => 5]]]
+		];
+		$collection = (new Collection($items))->listNested('stuff');
+		$this->assertEquals(range(1, 5), $collection->extract('id')->toArray(false));
+	}
+
 }