Question

Rails noob here. I have a rails application with (in this example) three tables. Users, Machines, and Tests.

Users have many Machines and Tests.

Machines belong to Users.

Tests belong to Machines.

When I create a new test, I want the field test.machine_id to automatically be set to the id of the machine that owns that test. I have been able to create a field with a drop-down menu showing all machines owned by current_user, but I don’t want the user to have to set this field manually.

Tests can only be created by accessing a “create new test” link on a Machine Show page.

*For example, User 1 has Machines 4 and 5. When viewing Machine 5’s Show page, I want to create test 10. I want test(10).machine_id to be set to 5 without a user having to enter this manually.*

In my tests_controller.rb file, I have the following:

 def new
@test = Test.new
@machines = current_user.machiness.all

respond_to do |format|
  format.html # new.html.erb
  format.xml  { render :xml => @test }
end
end


 def create
@test = Test.new(params[:test])

respond_to do |format|
  if @test.save
    format.html { redirect_to(@test, :notice => 'Test was successfully created.') }
    format.xml  { render :xml => @test, :status => :created, :location => @test }
  else
    format.html { render :action => "new" }
    format.xml  { render :xml => @test.errors, :status => :unprocessable_entity }
  end
end

end

I imagine I need something like:

def create
@test = current_machine.tests.build(params[:test])
...
end

…but I don’t think current_machine is an actual object.

Tests can only be created by accessing a “create new test” link on a Machine Show page.

Any suggestions?

Answer 1

Consider using a nested resource for your Test model. In your routes file, you would set up your resources like this:

resources :machines do
  resources :tests
end

This will make the route for a new Test look like /machines/:machine_id/tests/new. So now your link to the new Test page would look something like

<%= link_to "New Test", new_machine_tests_path(@machine) %>

and your new action in TestsController would be something like

def new
  @test = Test.new
  @machine = Machine.find(params[:machine_id])
  ...
end

Finally, the form for your nested Test resource would be something like

<%= form_for [@machine, @test] do |f| %>
...

That sets up the form to post to a path that will automatically include your machine_id, something /machines/123/tests.

So in the create action of your TestsController you can do something like

def create
  @test = Test.new(params[:test])
  @test.machine_id = params[:machine_id]
  ...
end