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module ActiveRecord
# Mixins are a way of decorating existing Active Record models with additional behavior. If you for example
# want to keep a number of Documents in order, you can include Mixins::List, and all of the sudden be able to
# call <tt>document.move_to_bottom</tt>.
module Mixins
# 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> if you want
# 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 ActiveRecord::Mixins::List
# 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 List
def self.append_features(base)
super
base.before_destroy :remove_from_list
base.after_create :add_to_list_bottom
end
# can be overriden
def position_column
"position"
end
# Moving around on the list
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
self.class.transaction do
decrement_positions_on_lower_items
assume_bottom_position
end
end
def move_to_top
self.class.transaction do
increment_positions_on_higher_items
assume_top_position
end
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
update_attribute position_column, self.send(position_column).to_i + 1
end
def decrement_position
update_attribute position_column, self.send(position_column).to_i - 1
end
# Querying the position
def first?
self.send(position_column) == 1
end
def last?
self.send(position_column) == bottom_position_in_list
end
private
# Overwrite this method to define the scope of the list changes
def scope_condition() "1" end
def higher_item
self.class.find_first(
"#{scope_condition} AND #{position_column} = #{(send(position_column).to_i - 1).to_s}"
)
end
def lower_item
self.class.find_first(
"#{scope_condition} AND #{position_column} = #{(send(position_column).to_i + 1).to_s}"
)
end
def bottom_position_in_list
item = bottom_item
item ? item.send(position_column) : 0
end
def bottom_item
self.class.find_first(
"#{scope_condition} ",
"#{position_column} DESC"
)
end
def assume_bottom_position
update_attribute position_column, bottom_position_in_list.to_i + 1
end
def assume_top_position
update_attribute position_column, 1
end
def decrement_positions_on_lower_items
self.class.update_all(
"#{position_column} = (#{position_column} - 1)", "#{scope_condition} AND #{position_column} > #{send(position_column).to_i}"
)
end
def increment_positions_on_higher_items
self.class.update_all(
"#{position_column} = (#{position_column} + 1)", "#{scope_condition} AND #{position_column} < #{send(position_column)}"
)
end
def increment_positions_on_all_items
self.class.update_all(
"#{position_column} = (#{position_column} + 1)", "#{scope_condition}"
)
end
end
end
end
|
