Make ActiveRecord defer/postpone saving the records you add to an habtm (has_and_belongs_to_many) or has_many association until you call model.save, allowing validation in the style of normal attributes.
gem install deferred_associations
class Room < ActiveRecord::Base
has_and_belongs_to_many_with_deferred_save :people
has_many_with_deferred_save :tables
validate :usage
before_save :check_change
def usage
if people.size > 30
errors.add :people, "There are too many people in this room"
end
if tables.size > 15
errors.add :tables, "There are too many tables in this room"
end
# Neither people nor tables are saved to the database, if a validation error is added
end
def check_change
# you can check, if there were changes to the association
if people != people_without_deferred_save
self.updated_at = Time.now.utc
end
end
end
Tested with Rails 2.3.14, 3.2.2 on Ruby 1.8.7, 1.9.3 and JRuby 1.6.6
Be aware, that the habtm association objects sometimes asks the database instead of giving you the data directly from the array. So you can get something like
room = Room.new
room.people << Person.create
room.people.first # => nil, since the DB doesn't have the association saved yet
http://github.com/MartinKoerner/deferred_associations/issues
Most of the code for the habtm association was written by TylerRick for his gem has_and_belongs_to_many_with_deferred_save Mainly, I changed two things:
- added ActiveRecord 3 compatibility
- removed singleton methods, because they interfere with caching
This plugin is licensed under the BSD license.
2012 (c) Martin Körner