Redirect to nested resource url in Rails

Sometimes in our developer lives we have to nest our resources. In my case I was nesting a Form within a User, the resulting routes file and url are:

~/config/routes.rb

Rails.application.routes.draw do
  resources :users do
    resources :forms
  end
end

And the resulting route structure:

/users/:user_id/forms/:id

I ran into an issue when updating a form, I was getting the error Undefined method or varaible form_path when trying to redirect to just the form, like the below example shows:

if @form.update(form_params)
  format.html { redirect_to @form, notice: "Form was successfully updated." }
end

What I had to do was update the redirect_to method to accept an array of resources, in this case both a user and form. The resulting working code is below:

if @form.update(form_params)
  format.html { redirect_to [@user, @form], notice: "Form was successfully updated." }
end

Just like the url this form was rendered from has both a user and a form, the redirect_to also needs a user and form to navigate successfully.

When you need to use the url path helper you can pass the objects in without the array brackets, like so:

redirect_to edit_user_form_path(@user, @form)