Creating associated object from collection select

Question

I have multiple Lessons and most of them have some prerequisites which are themselves other lessons. The Prerequisite model represents the relationship and each has a lesson_id and prerequisite_lesson_id.

class Lesson < ApplicationRecord
  has_many :prerequisites
  has_many :prerequisite_lessons, :through => :prerequisites
end

class Prerequisite < ApplicationRecord
  belongs_to :lesson
  belongs_to :prerequisite_lesson, :class_name => "Lesson"
end

I'm trying to figure out a way so that:

• When I create a new Lesson and select one or more prerequisites from a collection_select
• multiple Prerequisite objects are created based on what was selected, with the lesson_id being the created Lesson id.

Here is part of my Lesson controller:

def create
  @lesson = Lesson.new(lesson_params)

  if @lesson.save
    if @lesson.prerequisite_ids.length > 0
      @lesson.prerequisite_ids.each do |p|
        Prerequisite.new(lesson_id: @lesson.id, prerequisite_lesson_id: p)
      end
    end
    flash[:notice] = "Lesson created..."
    redirect_to root_url
  else
    render :new
  end
end

...

def lesson_params
  params.require(:lesson).permit(
    :name,
    :high_tempo,
    :low_tempo,
    :interval,
    :advance_tempo,
    prerequisites_attributes: [
      :lesson_id,
      :prerequisite_lesson_id
    ]
  )
end

and my form:

<%= f.collection_select(:prerequisite_ids, Lesson.all, :id, :name, {}, {:multiple => true}) %>

UPDATE:

In the logs, I see:

"lesson"=>{"name"=>"Lesson 6", "high_tempo"=>"200", "low_tempo"=>"100", "interval"=>"10", "advance_tempo"=>"140", "prerequisite_ids"=>["", "3", "4"]}, "commit"=>"Save"} Unpermitted parameter: prerequisite_ids'`

Answer 1

It looks like there are a couple of problems here:

One is that you are using Prerequisite.new(...) when I think you want to be using Prerequisite.create(...)

So your create action should be:

def create
  @lesson = Lesson.new(lesson_params)

  if @lesson.save
    if @lesson.prerequisite_ids.length > 0
      @lesson.prerequisite_ids.each do |p|
        Prerequisite.create(lesson_id: @lesson.id, prerequisite_lesson_id: p)
      end
    end
    flash[:notice] = "Lesson created..."
    redirect_to root_url
  else
    render :new
  end
end

The other is this (from your logs):

"lesson"=>{"name"=>"Lesson 6", "high_tempo"=>"200", "low_tempo"=>"100", "interval"=>"10", "advance_tempo"=>"140", "prerequisite_ids"=>["", "3", "4"]}, "commit"=>"Save"} Unpermitted parameter: prerequisite_ids'`

In your controller, you are permitting

def lesson_params
  params.require(:lesson).permit(
    :name,
    :high_tempo,
    :low_tempo,
    :interval,
    :advance_tempo,
    prerequisites_attributes: [
      :lesson_id,
      :prerequisite_lesson_id
    ]
  )
end

But note that your actual data is coming in as "lesson" => {..., "prerequisite_ids"=>["", "3", "4"]}

So you should instead permit like this:

def lesson_params
  params.require(:lesson).permit(
    :name,
    :high_tempo,
    :low_tempo,
    :interval,
    :advance_tempo,
    prerequisite_ids: []
  )
end

Additionally, it looks like your prerequisite_ids are including a value that is an empty string. Based on this post, it looks like you may need to add include_hidden: true to your select tag, like this:

<%= f.collection_select(:prerequisite_ids, Lesson.all, :id, :name, {}, {:multiple => true, include_hidden: true}) %>