Slick 2聚合-如何获得标量结果? [英] Slick 2 aggregation - how to get a scalar result?

问题描述

我有一个表，其中有一个Int列TIME:

I have a table with an Int column TIME in it:

def time = column[Int]("TIME")

表已映射为自定义类型.我想找到最大时间值，即执行简单的汇总. 文档中的示例似乎很容易:

The table is mapped to a custom type. I want to find a maximum time value, i.e. to perform a simple aggregation. The example in the documentation seems easy enough:

val q = coffees.map(_.price)
val q1 = q.min
val q2 = q.max

但是，当我这样做时，q1和q2的类型是Column[Option[Int]].我可以对此执行get或getOrElse以获得Column[Int]类型的结果(即使这对我来说似乎有些令人惊讶-是get的Column成员，还是从到Int，然后再次包装到Column?为什么?)，但是我无法使用标量值，当我尝试将其分配给Int时，出现一条错误消息:

However, when I do this, the type of q1 and q2 is Column[Option[Int]]. I can perform a get or getOrElse on this to get a result of type Column[Int] (even this seems somewhat surprising to me - is get a member of Column, or is the value converted from Option[Int] to Int and then wrapped to Column again? Why?), but I am unable to use the scalar value, when I attempt to assign it to Int, I get an error message saying:

type mismatch;
 found   : scala.slick.lifted.Column[Int]
 required: Int

如何从聚合查询中获取scala值?

How can I get the scala value from the aggregated query?

推荐答案

我的猜测是您没有调用调用程序，这就是为什么您获得Column对象的原因.试试这个:

My guess is that you are not calling the invoker that's the reason why you get a Column object. Try this:

val q1 = q.min.run

应返回Option[Int]，然后您可以get或getOrElse.

Should return an Option[Int] and then you can get or getOrElse.

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