Challenging Rails Question with Form Based on Existing Resources - ruby-on-rails

Question

You have a set of related models created through a scaffold e.g. a house, which has many rooms, which each have many windows, which each has a selection of locks.
These resources are already full of data i.e. someone has entered all the information, such as: a room called 'kitchen' has various windows associated with it and these windows each have five different locks associated with them.
Someone comes along and says:
Can you create a form that lets someone create a new project where they can select the different rooms, windows and then specify the locks that they would like for that project? (these are already in the system, nothing new to add, just the associations to a new project)
This sounds like a nested form but I have wasted a lot of time trying to solve this - there are many levels of nesting, which make this tricky. Any suggestions?

Answer 1

session based solution
With such deeply nested models select box on the front end wouldn't be enough...
Assuming this, you may want to create a current_house who's id live in a session (just like current_user works).
Once you have your current_house add different items by navigating to your list of items view and clicking on the add_to link :
# house_controller.rb
def add_to
current_house.polymorphic_items << Kitchen.find(params[:id])
redirect_to :back
end
But there are many approaches to this session based solution which sort of implements a cart/order system. You may want to add a current_item to add stuff in each leaf of your tree aka room of your house.
E.G after clicking on the kitchen you just added :
before_filter :set_current_item
def add_to
current_item.windows << Window.find(id)
end
current_item beeing polymorphic : a living room, a bathroom etc.
But how you implement that precisely depends on your Domain Model....
As a rule of thumb regarding nested forms I'd follow rails guidance for routes : don't go deeper than one level or you'll end up in a mess.

Answer 2

Yes this is a nested form. Railscasts nested forms is a great place to start.
If everything is already in the system you probably just want select boxes so they can select what they want. Also check out the .build method. If you have multiple levels of nesting you can also manually set the association by passing in the foreign key yourself.

Answer 3

I think you can model this with a single level of nested attributes, given the models below (based on Windows/Locks pre-existing and a room just needing to mix and match them into a set of windows with given locks):
class House < ActiveRecord::Base
has_many :rooms
end
class Room < ActiveRecord::Base
belongs_to :house
has_many :window_configs
end
class WindowConfig < ActiveRecord::Base
belongs_to :room
belongs_to :window
belongs_to :lock
end
class Lock < ActiveRecord::Base
has_many :window_configs
end
class Window < ActiveRecord::Base
has_many :window_configs
end
... based on that model setup, you could have a single house form that you dynamically add child 'room' definitions to that each have a name and a collection of window_configs which have two select boxes for each one (choose a window definition and then a lock definition). Because you're dynamically adding multiple rooms with multiple windows, you'd need some JS to populate new form elements, but it could all live in a single nested form.
form_for :house do |form|
# Dynamically add a Room form for each room you want with js
form.fields_for :room do |room_attributes|
room_attributes.text_field :name
# Dynamically add window_config forms on Room w/ JS
room_attributes.fields_for :window_config do |window_attributes|
window_attributes.select :window_id, Window.all
window_attributes.select :lock_id, Lock.all