嵌套协会/参与轨道 [英] Nested association/join in rails

问题描述

我有一个座对象，它有一个车对象，它有一个所有者具有名称。我想显示的车 品牌和车小号所有者的名称在一起。如何做到这一点在一个查询？

I have a seat object that has a car object that has a owner that has a name. I want to display the car brand and the car's owner's name together. How do I do this in one query?

例如：

class Seat < ActiveRecord::Base
  belongs_to :car

  def description
    "I am in a #{car.brand} belonging to #{car.owner.name}"
    # --> how do I replace this with one query?
  end
end

我会注意到，这是一个高度人为的例子，以简化我的问题。我这样做上千次成一排，因此需要更多的效益。

I'll note that this is a highly contrived example to simplify my question. I'm doing this thousands of times in a row, hence the need for more efficiency.

推荐答案

让我们说你是想查询座椅模式，并且要急于负载车和所有者对象，可以使用包括条款。

Let us say you are trying to query the Seat model, and you want to eager load the car and owner objects, you can use the includes clause.

Seat.includes(:car => :owner).where(:color => :red).each do |seat|
  "I am in a #{seat.car.brand} belonging to #{seat.car.owner.name}"
end

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