有代表和条件的活动记录 [英] Active Record with Delegate and conditions
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问题描述
可以在Active Record模型中使用委托，并使用之类的条件：if
Is it possible to use delegate in your Active Record model and use conditions like :if on it?
class User < ApplicationRecord
delegate :company, :to => :master, :if => :has_master?
belongs_to :master, :class_name => "User"
def has_master?
master.present?
end
end
推荐答案
否，你不能，但你可以通过：allow_nil =>
No, you can't, but you can pass the :allow_nil => true option to return nil if the master is nil.
class User < ActiveRecord::Base
delegate :company, :to => :master, :allow_nil => true
# ...
end
user.master = nil
user.company
# => nil
user.master = <#User ...>
user.company
# => ...
否则，您需要使用委托宏编写自己的自定义方法来更复杂选项。
Otherwise, you need to write your own custom method instead using the delegate macro for more complex options.
class User < ActiveRecord::Base
# ...
def company
master.company if has_master?
end
end
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