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