Rails 3.2 Updating Nested Attributes

Question

Here's my problem. If I go to Projects#edit, I am unable to change the course it is assigned to. If I attempt to create a new course for it, or choose from an existing one, I get the following error:

Couldn't find Course with ID=23 for Project with ID=62
app/controllers/projects_controller.rb:49:in `update'

{...
"project"=>{"title"=>"Sup",
"due_date"=>"2012-01-23",
"course_id"=>"27",                        # THIS IS THE ID OF THE NEW COURSE I WANT
"course_attributes"=>{"name"=>"Calc I",   # THIS IS THE OLD ONE, I don't need this. Why is it passing this?
"number"=>"MATH102",
"user_id"=>"3",
"id"=>"23"},
"description"=>"bla bla bla"},
"commit"=>"Update Project",
"user_id"=>"3",
"id"=>"62"}

So I can see that it's trying to pass in the course_attributes, but it's not actually setting the new course_id. I don't understand why course_attributes is being passed, the other form is blank, and the course_attributes being passed, are the attributes of the old course. I want to set the course_id to be the course_id being passed (27 in this case).

ProjectsController

def new
  @project  = @user.projects.new
  @courses = @user.courses    # Used to populate the collection_select
  @project.build_course       # I was informed I need to use this to get the form_for to work
end

def edit
  @project = Project.find(params[:id])
  @courses = @user.courses    # Used to populate the collection_select
end

def update
  @project = Project.find(params[:id])
  @courses = @user.courses

  if @project.update_attributes(params[:project])
    flash[:notice] = 'Project was successfully updated.'
    redirect_to user_projects_path(@user)
  else
    render :edit
  end
end

Line 49 is the call to update_attributes.

Other Information

project.rb

belongs_to :user
belongs_to :course

attr_accessible :course_id, :course_attributes
accepts_nested_attributes_for :course

course.rb

belongs_to :user
has_many :projects

user.rb

has_many :projects
has_many :courses

So a project has a course_id in the database. I'm currently creating or choosing an existing course on the fly on the Projects#new page. Here's my form for that. I use a JavaScript toggle to alternate between the collection_select and the two text_fields.

projects/new.html.haml

= form_for [@user, @project] do |f|
  # This is shown by default
  = f.collection_select :course_id, @courses, :id, :name, { prompt: true }

  .hidden # This is hidden by default and shown using a toggle
    = f.fields_for :course do |builder|
      = builder.text_field :name, class: 'large', placeholder: 'Ex: Calculus I'
      = builder.label :number, 'Number'
      = builder.text_field :number, class: 'new_project_course_number'
      = builder.hidden_field :user_id, value: current_user.id

Now, if I am on the new project page, and I attach it to a course by choosing an existing course, it will work correctly. The Project will be created, and the course_id will be set correctly.

If I am on the new project page, and I create a course by using my JavaScript toggle, then filling out the Course Name and Course Number, and click Create, then it will also work. The Course will be created, and the Project will be created with the correct course_id.

Sorry for the lengthy post, but I wanted to provide all information I could. Thanks!

UPDATE 1

routes.rb

resources :users do
  resources :projects do
    collection do
      get 'completed'
      match 'course/:course_number' => 'projects#course', as: 'course'
    end
  end

  resources :courses
end

Answer 1

Assuming that your Projects#edit form is similiar to your Projects#new

This is creating the course_attributes in params

  .hidden # This is hidden by default and shown using a toggle
    = f.fields_for :course do |builder|
      = builder.text_field :name, class: 'large', placeholder: 'Ex: Calculus I'
      = builder.label :number, 'Number'
      = builder.text_field :number, class: 'new_project_course_number'
      = builder.hidden_field :user_id, value: current_user.id

That's because if a user has a current course it will create fields for every course.

If you want to be able to build a new course on the fly in edit and new change this line to:

    = f.fields_for :course, @project.build_course(:user => @user) do |builder|

This will build a new course regardless of whether you're in edit or new. (Also you can remove @project.build_course in your controller this way.)

Answer 2

You don't list your routes, but assuming that is setup correctly, then the ProjectsController update should be able to do something like:

@course = Course.find(params[:course_id])