Dropdown Filter for Polymorphic association nested_attribute - drop-down-menu

Question

I'm building an application in which the user can create a Company and add Investments made to that company. The investments can come from two sources user's Funds or companies' Coinvestors. Funds are big deal in the application as the user can do a bunch of stuff in them. The Coinvestors are not that important, but I want to have control over few aspects of so I created a Model just for them. For that I created a Polymorphic association for which I gave the [terrible] name of Investables. I'm running Rails 3.2.15 and Ruby 2.0.0. Models are below:
class Company < ActiveRecord::Base
has_many :investments
accepts_nested_attributes_for :investments
end
class Investment < ActiveRecord::Base
belongs_to :fund, :class_name => "Fund", :foreign_key => 'investable_id'
belongs_to :company, inverse_of: :investments
belongs_to :coinvestor, :class_name => "Coinvestor", :foreign_key => 'investable_id'
end
class Fund < ActiveRecord::Base
has_many :investments, :as => :investable, :dependent => :destroy
end
class Coinvestor < ActiveRecord::Base
has_many :investments, :as => :investable, :dependent => :destroy
end
When editing the company I want to be able to add investments and I want to dynamically add form lines for each new investment. I was able to achieve that following the awesome 165-Edit Multiple Revised.
To make it more complex, I also want to add a Dropdown for choosing the Polymorphic Type so it filters the next Dropdown to show only the names of either the Funds or the Coinvestors.
For that I mostly adapted code from Railscast 88-Dynamic Select Menus(Thanks Ryan!!)
/views/company/edit.html.erb
<%= form_for(#company) do |f| %>
...
<%= f.fields_for :investments do |builder| %>
<%= render 'investment_fields', f: builder %>
<% end %>
<%= link_to_add_fields "Add Investment", f, :investments, 'table' %>
/views/company/_investment_fields.html.erb
<%= f.select :investable_type , [ "Fund", "Coinvestor" ], {prompt: "Investor Type"} %>
<%= f.grouped_collection_select( :investable_id, investables_to_collection, :investables, :name, :id, :name, {prompt: "Investor"} ) %>
The "investable_to_collection" is a helper I built to aggregate objects from both Funds and Coinvestors models.
module CompaniesHelper
InvestableCollection = Struct.new(:name, :investables)
CollectionItem = Struct.new(:name, :id)
def investables_to_collection
a = Array.new
a << InvestableCollection.new('Fund', Fund.all.map { |item| CollectionItem.new(item.name, item.id )})
a << InvestableCollection.new('Coinvestor', Coinvestor.all.map { |item| CollectionItem.new(item.name, item.id )})
a
end
end
I didn't add any JavaScript yet to filter the dropdown which will be another challenge. But I've got my beautiful view to show data I've already got in the DB. But the dropdown that should show the Fund's or Coinvestor's name is mixing up things: it will show the name of Coinvestor with ID == 1 even if the investment was made by a Fund.
I thought of making one of the models to have a custom ID such as f1, f2, f3 ... instead of 1, 2, 3... so the system wouldn't mix them. But it seems that it would generate other big compatibility issues.
Do you guys have any other idea?

Answer 1

I wouldn't alter the id column (i.e. I wouldn't change it from an auto-incrementing integer), but because you're mixing two lists in the DB into a single list in the UI you will need some way to note which table each item in the UI came from. For that, sure, use whatever ID scheme you want and then use that differentiating ID as the way to lookup the relevant item.
Also, if you're not going to use the auto-incrementing id columns in the UI (for links or whatever), then you could also just remove them and replace them with your custom identification scheme. There's no reason, for example, that you couldn't assign them all a random 8-digit number, ensuring that number is unique across the different types you're going to put into the list, and then using that id in the UI. It seems that the real issue you're running into is how to combine the lists where ids might overlap, and perhaps it may be feasible for you to devise a way to assign a non-overlapping ID.
Another possibility for assigning non-overlapping IDs, without having to come up with your own scheme or checking for uniqueness across multiple tables is to use a UUID for the lookup ID in the UI drop-down.