Rails odd error when submitting collection_select w/ unrelated validation

Question

I've got a working form that properly saves all attributes including a collection_select. However, when I add validates :title, presence: true and try to submit, I get

undefined method 'map' for nil:NilClass

My new action:

class ItemsController < ApplicationController
  def new
    @item = Item.new
    @categories = Question.editable_by(current_user)
    respond_to do |format|
      format.html { render :layout => true}
      format.json { render :json => @item  }
      format.js
    end

  end
end

View is items\_form.html.haml

Does not work

= f.collection_select :question_id, @categories, :_id, :iqs_item

Works

= f.collection_select :question_id, Question.editable_by(current_user), :_id, :iqs_item

This works when I add the @categories object from the controller to the view. I'm guessing something doesn't get passed for the error function in the view or it can't map the select when it tries to redraw the page with errors??

Please assist. Again, I can get it to work, but I'd rather not be putting method calls in the view.

Answer 1

= f.collection_select :question_id, @categories, :_id, :iqs_item

line would give undefined method 'map' for nil:NilClass error when collection given to it ,i.e., @categories is set as nil.

Add below mentioned code in the view, if your page displays successfully(without error message) and without a select then you know that @categories was set as nil.

- unless @categories.nil?
    = f.collection_select :question_id, @categories, :_id, :iqs_item

EDIT

Also set @categories in the create method