Expose more information about validation errors in Rails

active_model_errors_extension.rb

module ActiveModel
  class Errors
    def error_types
      @_error_types ||= Hash.new { |hash, key| hash[key] = [] }
    end

    def add_with_save_names(attribute, message = nil, options = {})
      message ||= :invalid
      message = message.call if message.is_a?(Proc)
      error_types[attribute] << message
      add_without_save_names(attribute, message, options)
    end

    def to_representable
      errors        = self
      error_types   = errors.error_types.dup
      full_messages = errors.old_full_messages.dup
      error_types.each_key { |key| error_types[key].uniq! }

      errors_as_struct = []

      errors.messages.each do |attribute_key, error_messages|
        error_messages.uniq.each do |error_message|
          full_message = full_messages.shift
          attribute    = full_message.gsub(error_message, '').strip
          attribute    = attribute.gsub(/\[\d+\]/, "")

          errors_as_struct <<
            OpenStruct.new(attribute:     attribute,
                           message:       error_message,
                           error_code:    error_types[attribute_key].shift,
                           attribute_key: attribute_key)
        end
      end

      errors_as_struct
    end

    alias_method_chain :add, :save_names
  end
end

errors.rb

module Representers
  module Errors
    module Collection

      include Roar::Representer::JSON::HAL

      property :time,             getter: proc { DateTime.now.utc }
      property :http_status_code, getter: proc { |options|
        options[:http_status_code] }

      collection :errors, {
        :extend => Representers::Errors::Resource,
        :getter => proc { self.to_representable }
      }

    end
  end
end

module Representers
  module Errors
    module Resource

      include Roar::Representer::JSON::HAL

      #Intended for the end-user
      property :message
      property :attribute

      #Intended for the developer
      property :attribute_key
      property :details
      property :error_code

    end
  end
end