Declare a property on a model class. Properties are not typed by default. You can store anything in a property that can be serialized into JSON. If you want a property to be of a custom class you have to define it using the :type option.

example:

 class Book
   property :title
   property :year
   property :publisher, type: Publisher
   property :published_at, default: -> { Date.current }
   property :next_year, default: ->(book) { book.year + 1 }
 end

returns all the property names of a model class that have been defined using the property method

example:

 class Book
   property :title
   property :year
 end
 Book.property_names # => [:title, :year]