UPDATE: This has finally been packaged into a proper plugin on Github. See: http://github.com/SFEley/habtm_list/
Bit rough and ready but works alright for me. Until someone creates a nicer plugin, you’ll need to cut and paste code from this page into two new files.
Note that to grab code from a wiki, you need to ‘edit’ the page below and capture the raw code between the pre tags. Then back out without saving. If you grab the HTML, double equals will disappear, and quotes will be converted into the wrong characters.
Create a new file at vendor/plugins/habtm_list/lib/habtm_list.rb and paste
module RailsExtensions
module HabtmList
def self.append_features(base) #:nodoc:
super
base.extend(ClassMethods)
base.class_eval do
class << self
alias_method :has_and_belongs_to_many_without_list_handling, :has_and_belongs_to_many
alias_method :has_and_belongs_to_many, :has_and_belongs_to_many_with_list_handling
end
end
end
module ClassMethods
def has_and_belongs_to_many_with_list_handling(name, options={})
if options.delete(:list)
options[:extend] = RailsExtensions::HabtmList::AssociationListMethods
after_add_callback_symbol = "maintain_list_after_add_for_#{name}".to_sym
before_remove_callback_symbol = "maintain_list_before_remove_for_#{name}".to_sym
options[:after_add] ||= []
options[:after_add] << after_add_callback_symbol
options[:before_remove] ||= []
options[:before_remove] << before_remove_callback_symbol
class_eval <<-EOV
def #{after_add_callback_symbol}(added)
self.#{name}.add_to_list_bottom(added)
end
def #{before_remove_callback_symbol}(removed)
self.#{name}.remove_from_list(removed)
end
EOV
end
has_and_belongs_to_many_without_list_handling(name, options)
end
end
module AssociationListMethods
def move_to_position(item, position)
return if !in_list?(item) || position.to_i == list_position(item)
list_item_class.transaction do
remove_from_list(item)
insert_at_position(item, position)
end
resort_array
end
def move_lower(item)
list_item_class.transaction do
lower = lower_item(item)
return unless lower
decrement_position(lower)
increment_position(item)
end
resort_array
end
def move_higher(item)
list_item_class.transaction do
higher = higher_item(item)
return unless higher
increment_position(higher)
decrement_position(item)
end
resort_array
end
def move_to_bottom(item)
return unless in_list?(item)
list_item_class.transaction do
decrement_positions_on_lower_items(item)
assume_bottom_position(item)
end
resort_array
end
def move_to_top(item)
return unless in_list?(item)
list_item_class.transaction do
increment_positions_on_higher_items(item)
assume_top_position(item)
end
resort_array
end
# should only be called externally from the before_remove callback
def remove_from_list(item)
decrement_positions_on_lower_items(item) if in_list?(item)
item[position_column] = nil
end
def first?(item)
item == self.first
end
def last?(item)
item == self.last
end
def higher_item(item)
return nil unless in_list?(item)
self.find(:first, :conditions => "#{position_column} = #{(list_position(item) - 1).to_s}")
end
def lower_item(item)
return nil unless in_list?(item)
self.find(:first, :conditions => "#{position_column} = #{(list_position(item) + 1).to_s}")
end
def in_list?(item)
self.include?(item)
end
def add_to_list_bottom(item)
item.save! if item.id.nil? # Rails 2.0.2 - Callbacks don't save first on association.create()
list_item_class.transaction do
assume_bottom_position(item)
end
resort_array
end
def add_to_list_top
list_item_class.transaction do
increment_positions_on_all_items
assume_top_position(item)
end
resort_array
end
# "First aid" method in case someone shifts the array around outside these methods, or
# the positions in the joins table go totally out of whack. Don't use it for
# simple ordering because it's inefficient.
def reset_positions
self.each_index do |i|
item = self[i]
connection.update(
"UPDATE #{join_table} SET #{position_column} = #{i} " +
"WHERE #{foreign_key} = #{@owner.id} AND #{list_item_foreign_key} = #{item.id}"
)
end
end
private
def position_column
@reflection.options[:order] || 'position'
end
def list_item_class
@reflection.klass
end
def join_table
@reflection.options[:join_table]
end
def foreign_key
@reflection.primary_key_name
end
def list_item_foreign_key
@reflection.association_foreign_key
end
def list_position(item)
self.index(item)
end
def set_position(item, position)
connection.update(
"UPDATE #{join_table} SET #{position_column} = #{position} " +
"WHERE #{foreign_key} = #{@owner.id} AND #{list_item_foreign_key} = #{item.id}"
)
if @target
obj = @target.find {|obj| obj.id == item.id}
obj[position_column] = position if obj
end
end
def assume_bottom_position(item)
set_position(item, self.length - 1)
end
def assume_top_position(item)
set_position(item, 0)
end
def increment_position_by(item, increment)
return unless in_list?(item)
connection.update(
"UPDATE #{join_table} SET #{position_column} = #{position_column} + (#{increment}) " +
"WHERE #{foreign_key} = #{@owner.id} AND #{list_item_foreign_key} = #{item.id}"
)
if @target
obj = @target.find {|obj| obj.id == item.id}
obj[position_column] = obj[position_column].to_i + increment if obj
end
end
def increment_position(item)
increment_position_by(item, 1)
end
def decrement_position(item)
increment_position_by(item, -1)
end
# This has the effect of moving all the higher items up one.
def decrement_positions_on_higher_items(position)
connection.update(
"UPDATE #{join_table} SET #{position_column} = (#{position_column} - 1) " +
"WHERE #{foreign_key} = #{@owner.id} AND #{position_column} <= #{position}"
)
@target.each { |obj|
obj[position_column] = obj[position_column].to_i - 1 if in_list?(obj) && obj[position_column].to_i <= position
} if @target
end
# This has the effect of moving all the lower items up one.
def decrement_positions_on_lower_items(item)
return unless in_list?(item)
position = list_position(item)
connection.update(
"UPDATE #{join_table} SET #{position_column} = (#{position_column} - 1) " +
"WHERE #{foreign_key} = #{@owner.id} AND #{position_column} > #{position}"
)
@target.each { |obj|
obj[position_column] = obj[position_column].to_i - 1 if in_list?(obj) && obj[position_column].to_i > position
} if @target
end
# This has the effect of moving all the higher items down one.
def increment_positions_on_higher_items(item)
return unless in_list?(item)
position = list_position(item)
connection.update(
"UPDATE #{join_table} SET #{position_column} = (#{position_column} + 1) " +
"WHERE #{foreign_key} = #{@owner.id} AND #{position_column} < #{position}"
)
@target.each { |obj|
obj[position_column] = obj[position_column].to_i + 1 if in_list?(obj) && obj[position_column].to_i < position
} if @target
end
# This has the effect of moving all the lower items down one.
def increment_positions_on_lower_items(position)
connection.update(
"UPDATE #{join_table} SET #{position_column} = (#{position_column} + 1) " +
"WHERE #{foreign_key} = #{@owner.id} AND #{position_column} >= #{position}"
)
@target.each { |obj|
obj[position_column] = obj[position_column].to_i + 1 if in_list?(obj) && obj[position_column].to_i >= position
} if @target
end
def increment_positions_on_all_items
connection.update(
"UPDATE #{join_table} SET #{position_column} = (#{position_column} + 1) " +
"WHERE #{foreign_key} = #{@owner.id}"
)
@target.each { |obj|
obj[position_column] = obj[position_column].to_i + 1 if in_list?(obj)
} if @target
end
def insert_at_position(item, position)
remove_from_list(item)
increment_positions_on_lower_items(position)
set_position(item, position)
end
# called after changing position values so the array reflects the updated ordering
def resort_array
@target.sort! {|x,y| x[position_column].to_i <=> y[position_column].to_i} if @target
end
end
end
end
and then for vendor/plugins/habtm_list/init.rb:
require 'habtm_list' ActiveRecord::Base.class_eval do include RailsExtensions::HabtmList end
See background and example usage
Revision History
3/18/08: Rewrote several methods to be more robust. (There were a few obvious bugs, too much SQL where simple array methods would work, and too much reliance on item[position], which is only accessible if the item was first loaded from the association.) At some point soon I may make a proper plug-in out of this and put it up for download, if I can figure out how to find and credit the original author(s). — sfeley@gmail.com
Comments
It would be nice to see a brief example of how to use this code :
- Where the source file should be installed
- What (if anything) should be added to Model source files …etc