如何返回一个空的ActiveRecord的关系？ [英] How to return an empty ActiveRecord relation?

问题描述

如果我有一个lambda一个范围，它需要一个参数，根据参数的值，我可能会知道，不会有任何的比赛，但我还是想回到的关系，而不是一个空数组：

If I have a scope with a lambda and it takes an argument, depending on the value of the argument, I might know that there will not be any matches, but I still want to return a relation, not an empty array:

scope :for_users, lambda { |users| users.any? ? where("user_id IN (?)", users.map(&:id).join(',')) : [] }

我真正想要的是一个无的方法，一切的对面，即返回仍可链的关系，但结果在查询被短路。

What I really want is a "none" method, the opposite of "all", that returns a relation that can still be chained, but results in the query being short-circuited.

推荐答案

您可以添加一个名为范围无：

You can add a scope called "none":

scope :none, where(:id => nil).where("id IS NOT ?", nil)

这将会给你一个空的ActiveRecord ::关联

That will give you an empty ActiveRecord::Relation

您也可以将它添加到的ActiveRecord :: Base的在初始化（如果你想）：

You could also add it to ActiveRecord::Base in an initializer (if you want):

class ActiveRecord::Base
 def self.none
   where(arel_table[:id].eq(nil).and(arel_table[:id].not_eq(nil)))
 end
end

很多方法可以得到这样的事情，但肯定不是最好的办法，以保持在code基地。我已经使用范围：无重构和发现，我需要保证一个空的ActiveRecord ::关系很短的时间，当

Plenty of ways to get something like this, but certainly not the best thing to keep in a code base. I have used the scope :none when refactoring and finding that I need to guarantee an empty ActiveRecord::Relation for a short time.

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