Using submodel accessor (STI) on parent params for nested forms

Question

i have the following models:

class Order < ApplicationRecord
class Bill < Order
class Preorder < Order

class Detail < ApplicationRecord
class Metric < Detail
class Unit < Detail

the model Order accept nested attributes for Detail, an Order can be a Bill or a Preorder and Detail can be by Unit or by Metric

i'm using jsonb_accessor gem to create additional attributes for Unit and Metric

class Metric < Detail
    jsonb_accessor :data,
      height: :decimal,
      width: :decimal
end

class Unit < Detail
    jsonb_accessor :data,
      quantity: :decimal
end

in my view, i'm using Cocoon gem to generate fields for Unit or Metric

<%= link_to_add_association(I18n.t('activerecord.models.metric.add'), f, :details, data: {association_insertion_node: '#details', association_insertion_method: :append}, :class => "btn btn-success", 
wrap_object: Proc.new { |detail| detail.type = "Metric"; detail = Metric.new }) %>
<%= link_to_add_association(I18n.t('activerecord.models.unit.add'), f, :details, data: {association_insertion_node: '#details', association_insertion_method: :append}, :class => "btn btn-success",
wrap_object: Proc.new { |detail| detail.type = "Unit"; detail = Unit.new }) %>

and in my controller, i have this method to verify the params

def order_params(type)
  if type=="Bill"
    params.require(:bill).permit(:client_id, :type, :delivered, :paid, :total_paid, details_attributes: [:id, :total_price, :type, :data, :service_id, :_destroy])
  elsif type=="Preorder"
    params.require(:preorder).permit(:client_id, :type, :delivered, details_attributes: [:id, :total_price, :type, :data, :service_id, :_destroy])
  end
end

the form works near perfectly, it store all data i put in the form except for :width, :height, :quantity, when i put them in params, it give an error saying that these params do not belong to Detail model and when i put :data instead, the column still empty.

i'm considering, using column directly for parent model Detail instead of using jsonb_accessor, or separate views and controller for each Metric and Unit models but i keep these solutions as last resort because i want to keep the code Dryier and use less columns as possible

Answer 1

Imho the problem is you are using the association details which means that rails is trying to create/save a Detail. Instead you will have to use the respective associations for units and metrics so rails knows to create the correct object which has the respective jsonb_accessors to save correctly.

You can just add the associations in the model:

has_many :metrics 
has_many :units 

I get this is possibly not as clean in your UI (if everything is a detail you can just add/list them together). Another alternative is define all possible json-fields in your Detail model (but not entirely sure if that defeats the purpose of using them in the first place).