install-acts-as-list

# Task re-ordering

We're now going to add the ability to re-order a story's tasks by
drag-and-drop. There's support for this built into Hobo, so there's
not much to do. First we need the `acts_as_list` plugin.  Run

    $ rails plugin install git://github.com/swanandp/acts_as_list.git

vendor/plugins/acts_as_list/README

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+ActsAsList
+==========
+
+This acts_as extension provides the capabilities for sorting and reordering a number of objects in a list. The class that has this specified needs to have a +position+ column defined as an integer on the mapped database table.
+
+
+Example
+=======
+
+  class TodoList < ActiveRecord::Base
+    has_many :todo_items, :order => "position"
+  end
+
+  class TodoItem < ActiveRecord::Base
+    belongs_to :todo_list
+    acts_as_list :scope => :todo_list
+  end
+
+  todo_list.first.move_to_bottom
+  todo_list.last.move_higher
+
+
+Copyright (c) 2007 David Heinemeier Hansson, released under the MIT license

vendor/plugins/acts_as_list/Rakefile

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+require 'rake'
+require 'rake/testtask'
+
+desc 'Default: run acts_as_list unit tests.'
+task :default => :test
+
+desc 'Test the acts_as_ordered_tree plugin.'
+Rake::TestTask.new(:test) do |t|
+  t.libs << 'lib'
+  t.pattern = 'test/**/*_test.rb'
+  t.verbose = true
+end

vendor/plugins/acts_as_list/init.rb

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+$:.unshift "#{File.dirname(__FILE__)}/lib"
+require 'active_record/acts/list'
+ActiveRecord::Base.class_eval { include ActiveRecord::Acts::List }

vendor/plugins/acts_as_list/lib/active_record/acts/list.rb

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+module ActiveRecord
+  module Acts #:nodoc:
+    module List #:nodoc:
+      def self.included(base)
+        base.extend(ClassMethods)
+      end
+
+      # This +acts_as+ extension provides the capabilities for sorting and reordering a number of objects in a list.
+      # The class that has this specified needs to have a +position+ column defined as an integer on
+      # the mapped database table.
+      #
+      # Todo list example:
+      #
+      #   class TodoList < ActiveRecord::Base
+      #     has_many :todo_items, :order => "position"
+      #   end
+      #
+      #   class TodoItem < ActiveRecord::Base
+      #     belongs_to :todo_list
+      #     acts_as_list :scope => :todo_list
+      #   end
+      #
+      #   todo_list.first.move_to_bottom
+      #   todo_list.last.move_higher
+      module ClassMethods
+        # Configuration options are:
+        #
+        # * +column+ - specifies the column name to use for keeping the position integer (default: +position+)
+        # * +scope+ - restricts what is to be considered a list. Given a symbol, it'll attach <tt>_id</tt> 
+        #   (if it hasn't already been added) and use that as the foreign key restriction. It's also possible 
+        #   to give it an entire string that is interpolated if you need a tighter scope than just a foreign key.
+        #   Example: <tt>acts_as_list :scope => 'todo_list_id = #{todo_list_id} AND completed = 0'</tt>
+        def acts_as_list(options = {})
+          configuration = { :column => "position", :scope => "1 = 1" }
+          configuration.update(options) if options.is_a?(Hash)
+
+          configuration[:scope] = "#{configuration[:scope]}_id".intern if configuration[:scope].is_a?(Symbol) && configuration[:scope].to_s !~ /_id$/
+
+          if configuration[:scope].is_a?(Symbol)
+            scope_condition_method = %(
+              def scope_condition
+                self.class.send(:sanitize_sql_hash_for_conditions, { :#{configuration[:scope].to_s} => send(:#{configuration[:scope].to_s}) })
+              end
+            )
+          elsif configuration[:scope].is_a?(Array)
+            scope_condition_method = %(
+              def scope_condition
+                attrs = %w(#{configuration[:scope].join(" ")}).inject({}) do |memo,column| 
+                  memo[column.intern] = send(column.intern); memo
+                end
+                self.class.send(:sanitize_sql_hash_for_conditions, attrs)
+              end
+            )
+          else
+            scope_condition_method = "def scope_condition() \"#{configuration[:scope]}\" end"
+          end
+
+          class_eval <<-EOV
+            include ActiveRecord::Acts::List::InstanceMethods
+
+            def acts_as_list_class
+              ::#{self.name}
+            end
+
+            def position_column
+              '#{configuration[:column]}'
+            end
+
+            #{scope_condition_method}
+
+            before_destroy :decrement_positions_on_lower_items
+            before_create  :add_to_list_bottom
+          EOV
+        end
+      end
+
+      # All the methods available to a record that has had <tt>acts_as_list</tt> specified. Each method works
+      # by assuming the object to be the item in the list, so <tt>chapter.move_lower</tt> would move that chapter
+      # lower in the list of all chapters. Likewise, <tt>chapter.first?</tt> would return +true+ if that chapter is
+      # the first in the list of all chapters.
+      module InstanceMethods
+        # Insert the item at the given position (defaults to the top position of 1).
+        def insert_at(position = 1)
+          insert_at_position(position)
+        end
+
+        # Swap positions with the next lower item, if one exists.
+        def move_lower
+          return unless lower_item
+
+          acts_as_list_class.transaction do
+            lower_item.decrement_position
+            increment_position
+          end
+        end
+
+        # Swap positions with the next higher item, if one exists.
+        def move_higher
+          return unless higher_item
+
+          acts_as_list_class.transaction do
+            higher_item.increment_position
+            decrement_position
+          end
+        end
+
+        # Move to the bottom of the list. If the item is already in the list, the items below it have their
+        # position adjusted accordingly.
+        def move_to_bottom
+          return unless in_list?
+          acts_as_list_class.transaction do
+            decrement_positions_on_lower_items
+            assume_bottom_position
+          end
+        end
+
+        # Move to the top of the list. If the item is already in the list, the items above it have their
+        # position adjusted accordingly.
+        def move_to_top
+          return unless in_list?
+          acts_as_list_class.transaction do
+            increment_positions_on_higher_items
+            assume_top_position
+          end
+        end
+
+        # Removes the item from the list.
+        def remove_from_list
+          if in_list?
+            decrement_positions_on_lower_items
+            update_attribute position_column, nil
+          end
+        end
+
+        # Increase the position of this item without adjusting the rest of the list.
+        def increment_position
+          return unless in_list?
+          update_attribute position_column, self.send(position_column).to_i + 1
+        end
+
+        # Decrease the position of this item without adjusting the rest of the list.
+        def decrement_position
+          return unless in_list?
+          update_attribute position_column, self.send(position_column).to_i - 1
+        end
+
+        # Return +true+ if this object is the first in the list.
+        def first?
+          return false unless in_list?
+          self.send(position_column) == 1
+        end
+
+        # Return +true+ if this object is the last in the list.
+        def last?
+          return false unless in_list?
+          self.send(position_column) == bottom_position_in_list
+        end
+
+        # Return the next higher item in the list.
+        def higher_item
+          return nil unless in_list?
+          acts_as_list_class.find(:first, :conditions =>
+            "#{scope_condition} AND #{position_column} = #{(send(position_column).to_i - 1).to_s}"
+          )
+        end
+
+        # Return the next lower item in the list.
+        def lower_item
+          return nil unless in_list?
+          acts_as_list_class.find(:first, :conditions =>
+            "#{scope_condition} AND #{position_column} = #{(send(position_column).to_i + 1).to_s}"
+          )
+        end
+
+        # Test if this record is in a list
+        def in_list?
+          !send(position_column).nil?
+        end
+
+        private
+          def add_to_list_top
+            increment_positions_on_all_items
+          end
+
+          def add_to_list_bottom
+            if self[position_column].nil?
+              self[position_column] = bottom_position_in_list.to_i + 1 
+            else
+              increment_positions_on_lower_items(self[position_column])
+            end
+          end
+
+          # Overwrite this method to define the scope of the list changes
+          def scope_condition() "1" end
+
+          # Returns the bottom position number in the list.
+          #   bottom_position_in_list    # => 2
+          def bottom_position_in_list(except = nil)
+            item = bottom_item(except)
+            item ? item.send(position_column) : 0
+          end
+
+          # Returns the bottom item
+          def bottom_item(except = nil)
+            conditions = scope_condition
+            conditions = "#{conditions} AND #{self.class.primary_key} != #{except.id}" if except
+            acts_as_list_class.find(:first, :conditions => conditions, :order => "#{position_column} DESC")
+          end
+
+          # Forces item to assume the bottom position in the list.
+          def assume_bottom_position
+            update_attribute(position_column, bottom_position_in_list(self).to_i + 1)
+          end
+
+          # Forces item to assume the top position in the list.
+          def assume_top_position
+            update_attribute(position_column, 1)
+          end
+
+          # This has the effect of moving all the higher items up one.
+          def decrement_positions_on_higher_items(position)
+            acts_as_list_class.update_all(
+              "#{position_column} = (#{position_column} - 1)", "#{scope_condition} AND #{position_column} <= #{position}"
+            )
+          end
+
+          # This has the effect of moving all the lower items up one.
+          def decrement_positions_on_lower_items
+            return unless in_list?
+            acts_as_list_class.update_all(
+              "#{position_column} = (#{position_column} - 1)", "#{scope_condition} AND #{position_column} > #{send(position_column).to_i}"
+            )
+          end
+
+          # This has the effect of moving all the higher items down one.
+          def increment_positions_on_higher_items
+            return unless in_list?
+            acts_as_list_class.update_all(
+              "#{position_column} = (#{position_column} + 1)", "#{scope_condition} AND #{position_column} < #{send(position_column).to_i}"
+            )
+          end
+
+          # This has the effect of moving all the lower items down one.
+          def increment_positions_on_lower_items(position)
+            acts_as_list_class.update_all(
+              "#{position_column} = (#{position_column} + 1)", "#{scope_condition} AND #{position_column} >= #{position}"
+           )
+          end
+
+          # Increments position (<tt>position_column</tt>) of all items in the list.
+          def increment_positions_on_all_items
+            acts_as_list_class.update_all(
+              "#{position_column} = (#{position_column} + 1)",  "#{scope_condition}"
+            )
+          end
+
+          def insert_at_position(position)
+            remove_from_list
+            increment_positions_on_lower_items(position)
+            self.update_attribute(position_column, position)
+          end
+      end 
+    end
+  end
+end