Virtus + AM::Validations

gistfile1.rb

class ApprovalsController < ApplicationController
  def index
    query = ApprovalQuery.new(params)
    return render(json: {errors: query.errors.full_messages}, status: 422) unless query.valid?
    
    render json: Approval.apply_query(query)
  end
end

class ApprovalQuery < Query::Base
  include Query::Paging
  attribute :customer_id, Integer
  attribute :incident_id, Integer
  attribute :filter, String, default: 'all'
  attribute :state, String, default: 'none'

  validates :filter, inclusion: %w(pending all unhandled)
  validates :state, inclusion: %w(none approved rejected postponed)
end

module Query
  class Base
    include ActiveModel::Model
    include Virtus.model
  end
end

module Query
  module Paging
    extend ActiveSupport::Concern

    included do
      attribute :page, Integer, default: 1
      attribute :per_page, Integer, default: proc{ default_page_size }

      validates :page, numericality: {greater_than: 0}
      validates :per_page, numericality: {greater_than: 0, less_than_or_equal_to: 100}
    end

    def offset
      (page - 1) * per_page
    end

    def apply(query)
      query.limit(per_page).offset(offset)
    end

    module ClassMethods
      def default_page_size
        30
      end
    end
  end
end