Rails: validate presence of parent_id in has_many association - ruby-on-rails

Question

I have a projects resource that has many tasks. I want to ensure that every task has a project_id by adding validates_presence_of :project_id to the tasks model.
However, when creating a new project with tasks, the project_id won't be available until the record saves, therefore I can't use validates_presence_of :project_id.
So my question is, how do I validate presence of project_id in the task model? I want to ensure every task has a parent.
...
class Project < ActiveRecord::Base
has_many :tasks, :dependent => :destroy
accepts_nested_attributes_for :tasks, :allow_destroy => true
...
class Task < ActiveRecord::Base
belongs_to :project
validates_presence_of :project_id

Answer 1

Your code works:
If you validates_presence_of :project, then as long as the project is there, it will validate. But if your project is unsaved, you could still save the task.
If you validates_presence_of :project_id, then the integer must be there, indicating a saved value.
Here's rSpec that proves the point. If you validate :project_id, you can't save a task without saving the Project.
class Task < ActiveRecord::Base
belongs_to :project
end
/specs/model_specs/task_spec.rb
require File.dirname(__FILE__) + '/../spec_helper'
describe Task do
before(:each) do
#project = Project.new
end
it "should require a project_id, not just a project object" do
task = Task.new
task.project = #project
Task.instance_eval("validates_presence_of :project_id")
task.valid?.should == false
end
it "should not be valid without a project" do
task = Task.new
task.project = #project
Task.instance_eval("validates_presence_of :project")
task.valid?.should == false
task.save.should == false
end
end

Answer 2

See here for the definitive answer :
class Project < ActiveRecord::Base
has_many :tasks, :dependent => :destroy, :inverse_of => :project
accepts_nested_attributes_for :tasks, :allow_destroy => true
class Task < ActiveRecord::Base
belongs_to :project
validates_presence_of :project
Not so elegant if you ask me... It should transparently validate.

Answer 3

Maybe I don't understand something, but it looks like you are trying to cheat rails. Why don't you just do like this:
class Task < ActiveRecord::Base
belongs_to :project
validate_presence_of :project
end

Answer 4

Take a look at this:
https://rails.lighthouseapp.com/projects/8994/tickets/2815-nested-models-build-should-directly-assign-the-parent
One thing I have done in the past is add: validates_presence_of :parent_id, :on => :update. Not great but it helps tighten the net a little.

Answer 5

I think you're having the same issue I dealt with. I have two models, Account and User, and when the account is created the first user is created through a #account.users.build. The User model has a validates_presence_of :account validation.
To make the first user pass validation, I added the following code to my Account model:
before_validation_on_create :initialize_users
def initialize_users
users.each { |u| u.account = self }
end

Answer 6

In reality you need both:
validates_presence_of project
validates_presence_of project_id
That way the task will not be saved in either of the following cases assuming that you have only 2 valid projects in the database, i.e. project id 99 is invalid:
task.project_id = 99
task.save
task.project = Project.new
task.save
I hope this is of help to someone.

Answer 7

Your Project class must define
accepts_nested_attributes_for :tasks
See Nested Model Form on Railscasts for more details on how to make the form.
EDIT:
In your form you should have something like this:
_form.html.erb
<% form_for #project do |f| %>
# project fields...
<% f.fields_for :tasks do |builder| %>
<%= render 'task_fields', :f => builder %>
<% end %>
<p><%= link_to_add_fields "Add task", f, :tasks %></p>
<%= f.submit %>
<% end %>
_task_fields.html.erb
<%= f.label :name, "Task name:" %>
<%= f.text_field :name %>
# task fields...
<%= link_to_remove_fields "Delete task", f, :tasks %>
link_to_add_fields and link_to_remove_fields are methods defined in application_helper to add/delete fields dynamically.