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module ActiveRecord
module Acts #:nodoc:
module List #:nodoc:
def self.append_features(base)
super
base.extend(ClassMethods)
end
# This act provides the capabilities for sorting and reordering a number of objects in 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 "_id"
# (if that hasn't been already) 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
if #{configuration[:scope].to_s}.nil?
"#{configuration[:scope].to_s} IS NULL"
else
"#{configuration[:scope].to_s} = \#{#{configuration[:scope].to_s}}"
end
end
)
else
scope_condition_method = "def scope_condition() \"#{configuration[:scope]}\" end"
end
class_eval <<-EOV
include ActiveRecord::Acts::List::InstanceMethods
def position_column
'#{configuration[:column]}'
end
#{scope_condition_method}
after_destroy :remove_from_list
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
def insert_at(position = 1)
insert_at_position(position)
end
def move_lower
return unless lower_item
self.class.transaction do
lower_item.decrement_position
increment_position
end
end
def move_higher
return unless higher_item
self.class.transaction do
higher_item.increment_position
decrement_position
end
end
def move_to_bottom
return unless in_list?
self.class.transaction do
decrement_positions_on_lower_items
assume_bottom_position
end
end
def move_to_top
return unless in_list?
self.class.transaction do
increment_positions_on_higher_items
assume_top_position
end
end
def remove_from_list
decrement_positions_on_lower_items if in_list?
end
def increment_position
return unless in_list?
update_attribute position_column, self.send(position_column).to_i + 1
end
def decrement_position
return unless in_list?
update_attribute position_column, self.send(position_column).to_i - 1
end
def first?
return false unless in_list?
self.send(position_column) == 1
end
def last?
return false unless in_list?
self.send(position_column) == bottom_position_in_list
end
def higher_item
return nil unless in_list?
self.class.find(:first, :conditions =>
"#{scope_condition} AND #{position_column} = #{(send(position_column).to_i - 1).to_s}"
)
end
def lower_item
return nil unless in_list?
self.class.find(:first, :conditions =>
"#{scope_condition} AND #{position_column} = #{(send(position_column).to_i + 1).to_s}"
)
end
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
self[position_column] = bottom_position_in_list.to_i + 1
end
# Overwrite this method to define the scope of the list changes
def scope_condition() "1" end
def bottom_position_in_list(except = nil)
item = bottom_item(except)
item ? item.send(position_column) : 0
end
def bottom_item(except = nil)
conditions = scope_condition
conditions = "#{conditions} AND id != #{except.id}" if except
self.class.find(:first, :conditions => conditions, :order => "#{position_column} DESC")
end
def assume_bottom_position
update_attribute(position_column, bottom_position_in_list(self).to_i + 1)
end
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)
self.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?
self.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?
self.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)
self.class.update_all(
"#{position_column} = (#{position_column} + 1)", "#{scope_condition} AND #{position_column} >= #{position}"
)
end
def increment_positions_on_all_items
self.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
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