通过Rails中的belongs_to的关系查询记录

问题描述：

我有一个活动的模式，他们belong_to一个位置

I have an Activities model, and they belong_to a Location

我该如何选择，其location.country =澳大利亚所有的活动？（例如）

How do i select all the activities whose location.country = Australia? (for example)

我可以做这样的范围之内？

Can I do this within a scope?

答

你所谈论的是一个连接的一种查询。您可以尝试在控制台中像这样的查询，如：

The kind of query you're talking about is a join. You can try queries like this in the console like:

Activity.joins(:locations).where('locations.country = "Australia"')

这意味着，SQL是要采取一切与当时有关的活动和地点，找到地点，其中国家=澳大利亚，然后返回你与那些位置相关的活动。

This means that SQL is going to take all the activities and locations associated with then, find the locations where country=Australia, and then return you the activities that are associated with those locations.

要使它成为一个更可重复使用的范围，对全国的变量在模型中定义的：

To make this into a more reusable scope, define it on your model with a variable for country:

scope :in_country, lambda {|country| joins(:locations).where('locations.country = ?',country)}

您可以了解更多有关这方面的 API文档。

You can learn more about this in the API docs.

通过Rails中的belongs_to的关系查询记录

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