ruby-on-rails - 定义一个方法来捕获类中的a_method[]

Question

我有很多这样的电话:

User.active[0..5]

哪个调用:

class User
  def active
     (an ActiveRelation)
  end
end

出于性能原因，我正在尝试做这样的事情:

class User
  def active[limit]
     (an ActiveRelation).limit(limit.to_a.size)
  end
end

不幸的是它不起作用，有什么想法可以实现吗？

== 编辑

更清洁:

class RelationWithLimit < ActiveRecord::Relation
  def [] selector
    case selector
    when Integer
      self.offset(selector).limit(1)
    when Range
      self.offset(selector.to_a[0]).limit(selector.to_a.size)
    end
  end
end

class ActiveRecord::Base
  private 
    def self.relation #:nodoc:
      @relation ||= RelationWithLimit.new(self, arel_table)
      finder_needs_type_condition? ? @relation.where(type_condition) : @relation
    end
end

Answer 1

您可以拥有自己的 ActiveRelation 特殊子类

class UserReturnRelation < ActiveRecord::Relation
  def [] lim
    self.limit lim
  end
end

class User
  def active
     # Without knowing exactly what relation you are using
     # One way to instantiate the UserReturnRelation for just this call
     UserReturnRelation.new(self, arel_table).where("state = active")
  end
end

然后 User.active[5] 应该按预期工作。

编辑:添加了实例化信息。你可能想看看 Base#scoped和 Base#relation了解更多信息