Rails, JSONAPI, and strong_params, making them work

posts_controller.rb

# app/controllers/posts_controller.rb

class PostsController < ApplicationController
  include RestifyParam
  
  ...
  
  
  def post_params
    restify_param(:post).require(:post).permit(
      :id,
      :title,
      :body,
      comments: [
        :id,
        :body
      ]
    )
  end
  
end

restify_param.rb

# app/controllers/concerns/restify_param.rb

module RestifyParam
  extend ActiveSupport::Concern
  
  def restify_param(param_key)
    ActionController::Parameters.new(param_key => restify_value(param_key))
  end
  
  private
  
  def restify_value(param_key, value = params)
    if value == params
      value = params.clone
    end
    if value[:data]
      if value[:data].delete(:type) == param_key.to_s.pluralize
        new_params = ActionController::Parameters.new
        attributes = value[:data].has_key?(:attributes) ? value[:data][:attributes] : value[:data]
        attributes.transform_keys!(&:underscore)
        new_params.merge!(attributes)
        if value[:data].has_key? :relationships
          value[:data][:relationships].each do |k,v|
            if k.pluralize != k
              new_params["#{k}_id"] = v[:data][:id] #belongs_to
            else
              new_params[k.to_s.underscore+"_attributes"] = restify_value(k,v) #has_many
            end
          end
        end
        new_params
      end
    end
  end
  
end