Question

Here is my problem:

class Facility < ActiveRecord::Base
...
has_and_belongs_to_many :languages, :autosave => false, :join_table => 'facilities_languages'
... 
end

When I do something like this:

facility = Facility.find(1)
language = Language.find(1)
facility.languages << language

Rails always do the SQL request:

"INSERT INTO `facilities_languages` (`language_id`,`facility_id`) VALUES (1, 1)"

Is there a way to avoid database requests unless I call ‘facility.save’ ?

Apparently, :autosave option here does something else.

Answer 1

Your Problem is that you use has_and_belongs_to_many which isnt based on a Model so you cant access it as an Object. You could create a Model that is doing the associations and then you could create new objects of this association model. e.g.:

rails g scaffold JoinClass faculty_id:integer language_id:integer

In the Model

class JoinClass < ActiveRecord::Base
     belongs_to :faculty
     belongs_to :language
end

In the other models:

Faculty

class Faculty < ActiveRecord::Base
     has_many :join_classes
     has_many :languages, :though => :join_classes
end

Language

class Language < ActiveRecord::Base
     has_many :join_classes
     has_many :faculties, :through => :join_classes
end

Then you would be able to add associations by creating association objects which arent saved automaticly. For example you have a String containing ids that contains the ids of the language objects which should be associated called language_ids in the FacultyController:

language_ids.split(",").each do |language_id|
    JoinClass.create(:faculty_id => @faculty.id, :language_id => language_id)
end

Of cause this code should be conditioned and positioned after the save of faculty.