nested forms : update child foreign key - ruby-on-rails

Question

I have a nested association:
class User < ActiveRecord::Base
has_many :hostels
accepts_nested_attributes_for :hostels
end
class Hostel < ActiveRecord::Base
belongs_to :user
end
The form :
<%= form_for #user do |f| %>
<%= f.label :email %><br>
<%= f.text_field :email %>
<% f.object.hostels << #hostel -%>
<%= f.fields_for :hostels do |ff| %>
<%= ff.hidden_field :id %>
<% end -%>
<%= f.submit %>
<% end -%>
the controller
def create
#user = User.new(user_params)
raise #user.hostels.inspect
end
private
def user_params
params.require(:user).permit(:email, hostels_attributes: [:id])
end
I would like to relink existing records of hostels to new users by updating hostel foreign key. This way, it definitly don't work.
Tried update_only: true parameter to nested too.
Any ideas about the subject or am I totally wrong about trying to do the operation like that ?

Answer 1

you can use a multiple select for hotels in you form, then in the controller you must require hostel_ids.
Models:
class User < ActiveRecord::Base
has_many :hostels
end
class Hostel < ActiveRecord::Base
belongs_to :user
end
Form: where :name is what you see in your multiple select
<%= form_for #user do |f| %>
<%= f.label :email %><br>
<%= f.text_field :email %>
<%= f.label "Hostels" %><br>
<%= select_tag :hotel_ids, options_for_select(Hostel.all.map{|h| [h.name, h.id]}), { :multiple => true } %>
<%= f.submit %>
<% end %>
Controller:
def create
#user = User.new(user_params)
end
private
def user_params
params.require(:user).permit(:email, hostel_ids)
end
I did not test the code but must work well.