如何在Ruby on Rails的ActiveRecord查询中加入间接关联？ [英] How to join an indirect association in ActiveRecord query in Ruby on Rails?

问题描述

在Ruby on Rails应用程序中，我有一个模型 Instance ，该模型属于另一个模型 Zone 。 区域模型本身属于 Country 模型。我正在按以下方式获取一组 Instance 对象：

In my Ruby on Rails application, I have a model Instance which belongs to another model Zone. The Zone model itself belongs to Country model. I am fetching a set of Instance objects as follows:

scope :thisweek, -> { joins(:zone).where(zones: {created_at: ...}).includes(:zone)

我想加入 Country 到 Zone 和 Instance ，然后根据 zone.country.name 字段对结果 Instance 集进行排序。有人可以帮我吗？

I would like to join Country to Zone and Instance as well, and then sort the result Instance set based on the zone.country.name field. Anyone can help me please?

推荐答案

您可以尝试以下操作：

scope :this_week, proc do
  includes(zone: :country)
    .where(zones: {created_at: whatever})
    .order('countries.name ASC')
end

（我使用了执行/结束格式，以便在多行显示每条指令）

(I used the do/end format on purpose to show on multi-lines each instruction)

也，您应该了解以下内容：

Also, something you should know:

# if
Zone belongs_to :country
# then
Zone.includes(:country).where(countries: { id: 12 })
#                    ^               ^^
# but if
Zone has_many :countries
# then
Zone.includes(:countries).where(countries: { id: 12 })
#                     ^^               ^^

其中始终使用表名，但 includes / 使用模型中声明的关系名称。

The where always uses the table's name but includes/joins uses the relation's name as it was declared in the model.

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