MongoMapper OR clause on 2 columns - Rails 3.1.rc4

How to perform something like this:

User.where("private = 1 开发者_开发知识库OR beta = 0")

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See: http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24or

That translates to:

User.where(:$or => [{:private => 1}, {:beta => 0}])