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.
How to install
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.update_some_relation_data(people) end # you can also use the rails-internal changes hash if changes.include?("people") self.do_stuff! end end end
Tested with Rails 2.3.18, 3.2.22, 4.1.14, 4.2.6 on Ruby 1.9.3, 2.2.4, 2.3.1 and JRuby 1.7, JRuby 184.108.40.206
Note, that Rails 3.2.14 associations are partly broken under JRuby cause of https://github.com/rails/rails/issues/11595 You'll need to upgrade activerecord-jdbc-adapter to >= 1.3.0.beta1, if you want to use this combination.
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.create room.people << Person.create room.people.first # => nil, since the DB doesn't have the association saved yet
Also it is good to know, that the array you set to an association is stored there directly, so after setting a list, the typical association methods are not working:
room = Room.create room.people.klass # => Person room.people = [Person.first] room.people.klass # => undefined method klass for #Array:0x007fa3b9efc2c0`
If the association is changed, it's name is stored in the changes hash. Therefore, updated_at of the containing record will be set on the next update. If an association is updated with the same array again, if will not be marked as changed. But if the order is changed, it will be marked!
people = [Person.create, Person.create] room = Room.create room.people = [people.first, people.second] room.changed? # => true room.save! room.people = [people.first, people.second] room.changed? # => false room.save! room.updated_at # => is still the same as above room.people = [people.second, people.first] room.changed? # => true room.save! room.updated_at # => got touched!
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 compatibility for ActiveRecord 3 and 4
- removed singleton methods, because they interfere with caching
This plugin is licensed under the BSD license.
2016 (c) Martin Körner