Added getLeafs function (#12)

* Added getLeafs function

* Update README.md

* fix typo

* added test for getLeaves function

* add another test case

Author: khaledkhamis

README.md

@@ -67,6 +67,7 @@ Schema::create(
 
 - [Inserting and Updating new nodes](#inserting-and-updating-new-nodes)
 - [Getting tree nodes](#getting-tree-nodes)
+- [Finding Leaf nodes](#getting-leaf-nodes)
 - [Map from array](#map-from-array)
 - [Rendering tree](#rendering-tree)
 
@@ -111,6 +112,11 @@ Building tree structure on PHP side - if some nodes will be missing, these branc
 $treeRoot = $root->buildTree($root->findDescendants()->get())
 ```
 
+### Getting leaf nodes
+```php
+Tree::getLeafs();
+```
+
 ### Map from array
 
 Three new roots, first with descendants

src/Gzero/EloquentTree/Model/Tree.php

@@ -344,6 +344,17 @@ public static function getRoots()
         return static::whereNull(static::getTreeColumn('parent'));
     }
 
+ /**
+     * Gets all leaf nodes
+     *
+     * @return \Illuminate\Database\Eloquent\Builder
+     */
+    public static function getLeaves()
+    {
+        $parents  = static::select('parent_id')->whereNotNull('parent_id')->distinct()->get()->pluck('parent_id')->all();
+        return static::wherenotin('id',$parents);
+    }
+
     /**
      * @param null $name
      *

tests/Test.php

@@ -336,6 +336,41 @@ public function can_map_array()
         $this->assertEquals(4, Tree::find(5)->findAncestors()->count(), 'Expected numer of Ancestors'); // Most nested
     }
 
+     /**
+     * getting leaf nodes
+     *
+     * @test
+     */
+     public function get_leaf_nodes()
+	{
+	        extract($this->_createSampleTree());
+		$correct = [
+			$child2,
+			$child3,
+			$child1_1_1
+		];
+		foreach($root->getLeaves()->get() as $key=>$node )
+		{
+			$this->assertEquals($correct[$key]->toArray(),$node->toArray());
+		}
+	}
+
+
+    /**
+     * getting leaf nodes if the tree is only one node(root)
+     *
+     * @test
+     */
+     public function get_leaf_nodes_root_only()
+        {
+		$root= with(new Tree())->setAsRoot();
+		$correct = [
+			$root->toArray()		
+		];
+		$this->assertEquals($correct,$root->getLeaves()->get()->toArray());
+	}
+
+
     /**
      * Define environment setup.
      *