我的模型的型号列表。如何从数据库中加载，但限制列表中的项目有多少？ [英] My model has a list of models. How do I load it from the database but limit the number of items in the list?

问题描述

在我的Rails项目我有这样一个场景：一辆车可以有很多违规停车罚单（我用的ActiveRecord）。这是我仿照它

In my Rails project I have a scenario where a car can have many parking tickets (I am using ActiveRecord). This is how I modelled it

class Car < ActiveRecord::Base
  has_many :parkingTickets, :order => "partkingTickets.date DESC"
end

class ParkingTickets < ActiveRecord::Base
    belongs_to :Car
end

和我这是怎么检索数据：

And this is how I retrieve data:

@cars = Car.includes(:parkingTickets).order('ID, parkingTickets.date desc')

这工作。 但现在我想要得到的车只能从过去12个月（如果票证是年纪大了，我并不需要它）的门票。 有什么办法能恩preSS这种使用活动记录？我不想去取车和获取停车票，因为这是汽车的名单，所以我会做很多数据库调用...

This works. But now I want to get the car only with the tickets from the last 12 months (if the ticket is older, I do not need it). Is there any way to express this using active record? I would not like to fetch a car and the fetch the parking tickets because this is a list of cars, so I would make many DB calls...

谢谢！

推荐答案

A 其中，情况应该解决的问题：

A where condition should solve the issue:

@cars = Car.includes(:parkingTickets)
           .where('parkingTickets.date >= ?', 12.months.ago)
           .order('ID, parkingTickets.date desc')

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