如何将集合中的属性拉出到数组中

Question

如果我有一个如下所示的类，如何将每个实例的姓氏从一个集合中拉出一个数组？

class Person
  include :Mongoid::Document

  field :first_name
  field :middle_name
  field :last_name
  field :email_address

end

Person.all # What do I do after I have the collection?

Answer 1

Person.all.map(&:last_name)会这样做

Answer 2

从集合中返回数组：

Person.where(blah).collect(&:last_name)

An explanation of &:object

Answer 3

Person.where（...搜索...）仅。（：姓氏）

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