Setup a custom select option text field in collection_select

Contact belongs_to Company

add a public method to your model, in this case Contact Contact.rb ( Model )

def name_and_company
self.name + " - " + self.company.name
end

Usage ( note the use of :name_and_company )

<%= form.collection_select(:contact_id, Contact.all, :id, :name_and_company ) %>