“Finding” the “parent” object in a nested resource relationship?

Question

Say that I have two resources, Project and Task. A Project can have many Tasks; A Task belongs to one Project. Also say that I have Task nested under Project in routes.rb:

map.resources :projects do |project|
  project.resources :tasks
end

Can one programmatically discover this relationship? Basically, I need to dynamically load an arbitrary object, then figure out if it has a "parent", and then load that parent.

Any ideas?

Answer 1

Routing will not help you as this is only meant to be used the other way around. What you can do is aliasing the relationship with :parent:

class Task
  belongs_to :project
  alias :project :parent
end

And then use this relationship to detect if a parent object is available:

if object.respond_to?(:parent)
  # do something
end

Moreover, you can use polymorphic routes if the routes are set up correctly:

polymorphic_url([object.parent, object])

Answer 2

Your code above determines the relationship for the routes and helps generate the right helpers to create paths and such.

What you need to make sure is that the relationships are properly declared in your madels. In the project model you should have:

has_many :tasks

In your task model you should have:

belongs_to :project

Once you have set that up, you are ready to get what you want.

@task = Task.first

unless @task.project.blank?
  project_name = @task.project.name
end