How do I return only fields that are needed in Mongoid?

How do 开发者_StackOverflow中文版I perform a query that doesn't return the entire document, but only fields that I have specified?

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From the horse's mouth:

# Return only the first and last names of each person.
  Person.only(:first_name, :last_name)

Source: http://mongoid.org/docs/querying/criteria.html#only

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you can also use pluck

Person.all.pluck(:first_name, :last_name, :id)

http://www.rubydoc.info/github/mongoid/mongoid/Mongoid%2FContextual%2FMongo%3Apluck