I am trying to get a collection select from an another model and I keep getting the above error. Looked everywhere, got rails casts but nothing makes sense. _form.rb <%= f.label :city %><br /> <%= f.collection_select (:share ,:city_id, City.all , :id, :name ) %> It highlights 'form' on the error report <h1>New share</h1> <%= render 'form' %> <%= link_to 'Back', shares_path %> Here are my models... class Share include Mongoid::Document field :name, type: String field :type, type: String field :summary, type: String field :description, type: String field :city, type: String embedded_in :city has_many :category end class City include Mongoid::Document embedded_in :share field :name, type: String field :country, type: String attr_accessible :name, :city_id, :id end Searched everywhere and I cannot figure it out. It must be something silly.