Question

I’m new to ruby and rails and I’m wanting to following coding standards and conventions as best as possible, so I don’t pick up any bad habits. I have two models: Course and Location. A course belongs_to a location, as a course can only have one location. A location has_many courses, as a location could be shared by more than one course.

When creating a course, a location may already exist that is found by its ID. Or the location may not yet exist, in which case a new location record must be created. My Course controller has the following create action.

def create
  @course = Course.new(params[:course])

  if params[:course][:location][:id].blank?
    @course.location = Location.create(params[:course][:location])
  else
    @course.location = Location.find_by_id(params[:course][:location][:id])
  end

  @course.save

  respond_with @course
end

Note that this is a REST API that only responds with JSON. The javascript that makes the request posts a JSON array in the same format that would be returned by a GET request

{
  "course":
  {
    "title":"US History",
    "credits":"3",
    "max_students":"100",
    "location":
    {
      "id":"",
      "building":"Freedom Hall",
      "room":"301"
    }
  }
}

or

{
  "course":
  {
    "title":"US History",
    "credits":"3",
    "max_students":"100",
    "location":
    {
      "id":"12", # this is the only difference
      "building":"Freedom Hall",
      "room":"301"
    }
  }
}

1. Compared with all of the examples I’ve read, this code doesn’t look so elegant. Is there better way to factor it?
2. If Location.create raises an exception, will @course.save still be called? Do I need to use Location.create!?
3. Likewise, will validation errors end up in @course.errors even though the errors were on the Location model? Do I need to rescue from the exception so that I can return the errors to the client?

Thank you very much for any and all help!

Answer 1

You can clean that up by using find_or_initialize_by_id. This should work:

def create
  @course = Course.new(params[:course])
  @course.location = Location.find_or_initialize_by_id(params[:course][:location][:id],
                                                       params[:course][:location])
  @course.save
  respond_with @course
end

Regarding your second question, in your code as you have it @course.save will not be called if Location.create (or Location.find) raises an exception (because they would happen first). However, the way I have coded it above, the exception would happen at the same point in the code, when save is called, at which point the association is also saved.