Ruby-on-rails 如何在 Rails 3 中使用 includes() 进行 find()
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/3943554/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to do find() with includes() in Rails 3
提问by 99miles
I'm trying to do something like this, but it's not working. How would I do this in Rails 3?
我正在尝试做这样的事情，但它不起作用。我将如何在 Rails 3 中做到这一点？
Student.find(12).includes(:teacher)
回答by Robert Speicher
You just have to be more careful with the order of the methods in this case:
在这种情况下，您只需要更加注意方法的顺序：
Student.includes(:teacher).find(12)
回答by mind.blank
Old question I know but just in case this helps someone...
我知道老问题，但以防万一这有助于某人...
Doing something like @student = Student.includes(:teacher).where(:id => 12)returns an array and so then using something such as @student.iddoesn't work.
做类似@student = Student.includes(:teacher).where(:id => 12)返回一个数组的事情，然后使用诸如此类的东西@student.id不起作用。
Instead you could do:
相反，你可以这样做：
@student = Student.includes(:teacher).where(:id => 12).first
Although Student.includes(:teacher).find(12)should work, but you can use the whereversion if you need to search by other/multiple fields.
虽然Student.includes(:teacher).find(12)应该可以工作，但是where如果您需要按其他/多个字段进行搜索，您可以使用该版本。
回答by Ivailo Bardarov
Student.includes(:teacher).where(:id => 12)
should work.
应该管用。
Can we see your models ?
我们可以看看你们的模型吗？
回答by coder_tim
You could try "where" instead of "find":
你可以试试“where”而不是“find”：
Student.includes(:teacher).where(:id => 12)
回答by Zelenka
There is no sense to use findwith includes.
Eager loading helps us to load the associated records of the objects to prevent n+1 problem. With only one record you will never experience n+1 problem.
find与一起使用没有意义includes。Eager loading 帮助我们加载对象的关联记录，以防止 n+1 问题。只有一个记录，你永远不会遇到 n+1 问题。
