Slick 3.0.0 聚合查询 [英] Slick 3.0.0 Aggregate Queries

问题描述

我正在尝试对两个表进行复杂的查询.它们如下所示:

I'm trying to do a complex querying on two tables. They look like below:

表 1:

  id:
  name:
  table2Id:
  version:

表 2:

  id:
  comments:

假设我有合适的 Slick 类来表示这些表，我试图从满足以下条件的表 1 和表 2 中获取所有元素:

Assuming that I have the appropriate Slick classes that represents these tables, I'm trying to get all the elements from Table1 and Table 2 that satisfies the following condition:

Table1.table2Id === Table2.id and max(Table1.version)

我尝试了以下方法:

val groupById = (for {
  elem1 <- table1Elems
  elem2 <- table2Elems if elem1.id === elem2.id
} yield (elem1, elem2)).groupBy(_._1.id)

我知道我必须映射 groupById 并查找最大版本，但我没有正确理解语法！有什么帮助吗?

I know that I have to map the groupById and look for the max version, but I'm not getting the syntax right! Any help?

我需要的是与以下 SQL 查询等效的 Slick:

What I need is effectively Slick equivalent of the following SQL query:

SELECT * 
FROM t t1 
WHERE t1.rev = (SELECT MAX(rev) FROM t t2 WHERE t2.id = t1.id)

推荐答案

模拟:

SELECT * from t t1 WHERE t1.rev = (SELECT max(rev) FROM t t2 WHERE t2.id = t1.id)

尝试以下任一方法:

val q1 = for{
  t < table1 if t.rev === (
    table2.filter(_.id === t.id).map(_.rev).max
  )
} yield t

val q2 = table1.filter{t=> t.rev === (
  table2.filter(_.id === t.id).map(_.rev).max
)}.map(identity)

根据评论进行

val q = (for{
  t1 < table1; t2 <- table2 if t1.id === t2.id
} yield t1).orderBy(_.version.max).reverse.take(1)

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