From 64d11f0587677afbdda5fa6de117a2c2533aade1 Mon Sep 17 00:00:00 2001
From: Rodrigo Alvarez <papipo@gmail.com>
Date: Mon, 5 Jul 2010 22:22:03 +0800
Subject: [PATCH] Added support for parent_id setter with blank value

---
 lib/mongoid_acts_as_tree.rb | 10 ++++++++--
 test/test_tree.rb           |  9 +++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/lib/mongoid_acts_as_tree.rb b/lib/mongoid_acts_as_tree.rb
index e4fff75..1537d3e 100644
--- a/lib/mongoid_acts_as_tree.rb
+++ b/lib/mongoid_acts_as_tree.rb
@@ -31,8 +31,14 @@ def acts_as_tree(options = {})
 
 					self.class_eval do
 						define_method "#{parent_id_field}=" do | new_parent_id |
-							new_parent = self.class.find new_parent_id
-							new_parent.children.push self, false
+						  if new_parent_id.present?
+  							new_parent = self.class.find new_parent_id
+  							new_parent.children.push self, false
+  						else
+    						self.write_attribute parent_id_field, nil
+    						self[path_field] = []
+    						self[depth_field] = 0
+						  end
 						end
 					end
 
diff --git a/test/test_tree.rb b/test/test_tree.rb
index 2d53cd5..616d855 100644
--- a/test/test_tree.rb
+++ b/test/test_tree.rb
@@ -89,6 +89,15 @@ class TestMongoidActsAsTree < Test::Unit::TestCase
 			assert more_deep_child.ancestors.include? child
 			assert more_deep_child.ancestors.include? parent
 		end
+		
+		should "assign blank parent_id" do
+		  @child_1.parent_id = ''
+		  @child_1.save
+		  
+		  assert_nil @child_1.reload.parent_id
+		  assert_equal 0, @child_1.depth
+		  assert_equal [], @child_1.path
+	  end
 
     context "node" do
       should "have a root" do