Rails中的组合字段

User.select("CONCAT(first_name, ' ', last_name) AS full_name")

def full_name
  "#{first_name} #{last_name}"
end

class User< ActiveRecord::Base
  composed_of :full_name, class_name: "FullName", mapping: [%w(first_name first_name), %w(last_name last_name)]
end

class FullName
  attr_accessor :first_name, :last_name

  def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
  end

  def to_s
    "#{first_name} #{last_name}"
  end
end