Define Rails Model Persistent Attributes in Model File

I recently played with MongoDB in Rails using Mongoid. I like the ability to define attributes for models within the model file (as opposed to in migrations):

class Person
  include Mongoid::Document
  field :name, :type => String
  field :birthday, :type => Date
end

For projects that cannot use a schema-less database, does a similar feature exist? Any gems or plugins that generate sche开发者_JAVA百科mas from a similar syntax would be greatly appreciated.

Thanks.

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I think both MongoMapper and Mongoid took their ideas about this from Datamapper which also support those SQL database.