From 2d483af0d7c3d17f5b22b702bc93c95a9e7d99da Mon Sep 17 00:00:00 2001
From: David Heinemeier Hansson <david@loudthinking.com>
Date: Wed, 8 Dec 2004 15:39:22 +0000
Subject: Unofficially added ListMixin

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@82 5ecf4fe2-1ee6-0310-87b1-e25e094e27de
---
 .../lib/active_record/mixins/list_mixin.rb         | 154 +++++++++++++++++++++
 1 file changed, 154 insertions(+)
 create mode 100644 activerecord/lib/active_record/mixins/list_mixin.rb

diff --git a/activerecord/lib/active_record/mixins/list_mixin.rb b/activerecord/lib/active_record/mixins/list_mixin.rb
new file mode 100644
index 0000000000..9f964f11af
--- /dev/null
+++ b/activerecord/lib/active_record/mixins/list_mixin.rb
@@ -0,0 +1,154 @@
+module ActiveRecord
+  # This mixin provides the capabilities for sorting and reordering a number of objects in list.
+  # The class that has this mixin included needs to have a "position" column defined as an integer on
+  # the mapped database table. Further more, you need to implement the <tt>scope_condition</tt> that
+  # defines how to separate one list from another.
+  #
+  # Todo list example:
+  #
+  #   class TodoList < ActiveRecord::Base
+  #     has_many :todo_items, :order => "position"
+  #   end
+  #
+  #   class TodoItem < ActiveRecord::Base
+  #     include ListMixin
+  #     belongs_to :todo_list
+  #  
+  #     private
+  #       def scope_condition
+  #         "todo_list_id = #{todo_list_id}"
+  #       end
+  #   end
+  #
+  #   todo_list.first.move_to_bottom
+  #   todo_list.last.move_higher
+  #
+  module ListMixin
+    def self.append_features(base)
+      super
+      base.class_eval do
+        before_destroy :remove_from_list
+        after_create   :add_to_list_bottom
+      end
+    end
+
+    # Moving around on the list
+
+    def move_lower
+      return unless lower_item
+      lower_item.decrement_position
+      increment_position
+    end
+
+    def move_higher
+      return unless higher_item
+      higher_item.increment_position
+      decrement_position
+    end
+    
+    def move_to_bottom
+      decrement_positions_on_lower_items
+      assume_bottom_position
+    end
+
+    def move_to_top
+      increment_positions_on_higher_items
+      assume_top_position
+    end
+    
+
+    # Entering or existing the list
+    
+    def add_to_list_top
+      increment_positions_on_all_items
+    end
+
+    def add_to_list_bottom
+      assume_bottom_position
+    end
+
+    def remove_from_list
+      decrement_positions_on_lower_items
+    end
+
+
+    # Changing the position
+
+    def increment_position
+      self.position = position.to_i + 1
+      save
+    end
+    
+    def decrement_position
+      self.position = position.to_i - 1
+      save
+    end
+    
+    
+    # Querying the position
+    
+    def first?
+      self.position == 1
+    end
+    
+    def last?
+      self.position == bottom_position_in_list
+    end
+
+    private
+      # Overwrite this method to define the scope of the list changes
+      def scope_condition; end
+    
+      def higher_item
+        self.class.find_first(
+          "#{scope_condition} AND position = #{(position.to_i - 1).to_s}"
+        )
+      end
+    
+      def lower_item
+        self.class.find_first(
+          "#{scope_condition} AND position = #{(position.to_i + 1).to_s}"
+        )
+      end
+    
+      def bottom_position_in_list
+        item = bottom_item
+        item ? item.position : 0
+      end
+    
+      def bottom_item
+        self.class.find_first(
+          "#{scope_condition} ",
+          "position DESC"
+        )
+      end
+
+      def assume_bottom_position
+        self.position = bottom_position_in_list.to_i + 1
+        save
+      end
+      
+      def assume_top_position
+        self.position = 1
+        save
+      end
+      
+      def decrement_positions_on_lower_items
+        self.class.update_all(
+          "position = (position - 1)",  "#{scope_condition} AND position > #{position.to_i}"
+        )
+      end
+      
+      def increment_positions_on_higher_items
+        self.class.update_all(
+          "position = (position + 1)",  "#{scope_condition} AND position < #{position.to_i}"
+        )
+      end
+
+      def increment_positions_on_all_items
+        self.class.update_all(
+          "position = (position + 1)",  "#{scope_condition}"
+        )
+      end
+  end
+end
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