Rails/ActiveRecord: save changes to a model's associated collections

Question

Do I have to save modifications to individual items in a collection for a model, or is there a method I can call to save them when I save the model.

#save

Answer 1

You have to do this yourself

This isnt entirely true. You can use the "build" method which will force a save. For the sake of example assume that you have a Company model and Employees (Company has_many Employees). You could do something like:

acme = Company.new({:name => "Acme, Inc"})
acme.employees.build({:first_name => "John"})
acme.employees.build({:first_name => "Mary"})
acme.employees.build({:first_name => "Sue"})
acme.save

Would create all 4 records, the Company record and the 3 Employee records and the company_id would be pushed down to the Employee object appropriately.

Answer 2

You can configure ActiveRecord to cascade-save changes to items in a collection for a model by adding the :autosave => true option when declaring the association. Read more.

Example:

class Payment < ActiveRecord::Base
    belongs_to :cash_order, :autosave => true
    ...
end

Answer 3

This post can be useful: http://erikonrails.snowedin.net/?p=267

Erik describe how to use "accepts_nested_attributes_for" in the model and <% f.fields_for %> in the view to do the job.

Its detailed description can be found in: http://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html

Answer 4

You have to do this yourself. Active Record does not cascade save operations in has_many relations after the initial save.

You could automate the process with a before_save callback.

Answer 5

just do a rental.dvd.save after you increment the value or in the above case you could use

rental.dvd.increment!(:copies)

which will also automatically save, note the '!' on increment!