accepts_nested_attributes_for child association validation failing

Question

I'm using accepts_nested_attributes_for in one of my Rails models, and I want to save the children after creating the parent.

The form works perfectly, but the validation is failing. For simplicity's sake imagine the following:

class Project < ActiveRecord::Base
  has_many :tasks
  accepts_nested_attributes_for :tasks
end

class Task < ActiveRecord::Base
  belongs_to :project

  validates_presence_of :project_id
  validates_associated :project
end

And I am running:

Project.create!(
  :name => 'Something',
  :task_attributes => [ { :name => '123' }, { :name => '456' } ]
)

Upon saving the project model, the validation is failing on the tasks because they don't have a project_id (since the project hasn't been saved).

It seems like Rails is following the pattern below:

• Validate Project
• Validate Tasks
• Save Project
• Save Tasks

The pattern should be:

• Validate Project
• On Pass: Save Project and continue...
• Validate Tasks
  • On Pass: Save Tasks
  • On Fail: Delete Project (rollback maybe?)

So my question boils down to: How can I get Rails to run the project_id= (or project=) method and validation on the children (tasks) AFTER the parent (project) has been saved, but NOT save the parent (project) model if any child (task) is invalid?

Any ideas?

Answer 1

Use :inverse_of and validates_presence_of :parent. This should fix your validation problem.

   class Dungeon < ActiveRecord::Base
     has_many :traps, :inverse_of => :dungeon
   end

   class Trap < ActiveRecord::Base
     belongs_to :dungeon, :inverse_of => :traps
     validates_presence_of :dungeon
   end

http://apidock.com/rails/ActiveModel/Validations/HelperMethods/validates_presence_of

https://github.com/rails/rails/blob/73f2d37505025a446bb5314a090f412d0fceb8ca/activerecord/test/cases/nested_attributes_test.rb

Answer 2

Use this answer for Rails 2, otherwise see below for the :inverse_of answer

You can work around this by not checking for the project_id if the associated project is valid.

class Task < ActiveRecord::Base
  belongs_to :project

  validates_presence_of :project_id, :unless => lambda {|task| task.project.try(:valid?)}
  validates_associated :project
end

Answer 3

Only validate the relationship, not the ID:

class Task < ActiveRecord::Base
  belongs_to :project

  validates_presence_of :project
end

As soon as the association is populated, ActiveRecord will consider the validation to have succeeded, whether or not the model is saved. You might want to investigate autosaving as well, to ensure the task's project is always saved:

class Task < ActiveRecord::Base
  belongs_to :project, :autosave => true

  validates_presence_of :project
end