Added tree mixin and unit tests for all the mixins

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@156 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

1 files changed, 36 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/mixins/tree.rb b/activerecord/lib/active_record/mixins/tree.rb
new file mode 100644
index 0000000000..582aa09b4b
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+++ b/activerecord/lib/active_record/mixins/tree.rb
@@ -0,0 +1,36 @@
+module ActiveRecord
+  module Mixins
+    # Including this mixin if you want to model a tree structure by providing a parent association and an children 
+    # association. This mixin assumes that you have a column called parent_id
+    # 
+    #   class Category < ActiveRecord::Base
+    #     include ActiveRecord::Mixins::Tree
+    #   end
+    #   
+    #   Example : 
+    #   root
+    #    \_ child1 
+    #         \_ sub-child1
+    #
+    #   root      = Category.create("name" => "root")
+    #   child1      = root.children.create("name" => "child1")
+    #   subchild1   = child1.children.create("name" => "subchild1")
+    #
+    #   root.parent # => nil
+    #   child1.parent # => root
+    #   root.children # => [child1]
+    #   root.children.first.children.first # => subchild1
+    module Tree
+
+      def self.append_features(base)
+        super        
+
+        base.module_eval <<-associations
+          belongs_to  :parent,    :class_name => name, :foreign_key => "parent_id"        
+          has_many    :children,  :class_name => name, :foreign_key => "parent_id", :order => "id", :dependent => true
+        associations
+              
+      end  
+    end
+  end
+end
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