def as_json(options={})
#   options hash accepts four keys for better customization :only, :methods, :include, :except
#   so whenever such keys are found, we call super with those keys to provide response consisting only those keys
  if options.key?(:only) or options.key?(:methods) or options.key?(:include) or options.key?(:except)
    h = super(options)
  else
    h = super(only: [:picture, :age],
              methods: [:name],
              include: {:emails => { :only => [:id, :email] })
  end
end
# response when no options passed:
# ex. render json: @user
# user: {
#   picture: "url",
#   age: "20",
#   name: "some name",
#   emails: [
#     {
#       id: 1,
#       email: "somename@gmail.com"
#     },
#     {
#       id: 2,
#       email: "somename@yahoo.com"
#     }
#   ]
# }
# response when options passed
# ex:   render json: @user.as_json(only: [:picture, :age], methods: [:name])
# user: {
#   picture: "url",
#   age: "20",
#   name: "some name"
# }