ScalaQuery多對多

Question

有沒有人有一個想法，如何在Scala Query中存檔多人到多人？

我想將博客帖子連接到一系列標籤。
這是我的數據庫設計：

我已經與我的自定義代碼成功，但檢查斯卡拉Querys生成的SQL當我不開心我的解決方案。
我玩過一種功能性的方法，它產生了許多SQL查詢，導致很多往返。
我可以弄清楚如何減少大約一半的查詢次數。

一個手工製作的查詢獲取我所有的數據很好地格式化在一個查詢，

select 
    p.id, p.content, p.posted_date, GROUP_CONCAT(t.name) 
from 
    post p, 
    tag t, 
    tag_post tp 
where 
    tp.post_id = p.id and tp.tag_id = t.id 
group by 
    p.id 

從斯卡拉查詢生成的查詢給予同樣的數據。

SELECT `t1`.`id`,`t1`.`content`,`t1`.`posted_date` FROM `post` `t1` 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=2) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=3) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=4) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=5) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=6) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=7) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=8) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=9) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=10) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=11) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=12) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=13) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=14) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=15) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=16) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=17) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=2) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=18) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=19) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=1) 
SELECT `t1`.`id`,`t1`.`name` FROM `tag` `t1` WHERE (`t1`.`id`=3) 
SELECT `t1`.`tag_id` FROM `tag_post` `t1` WHERE (`t1`.`post_id`=20) 

我擔心所有這些往返行程可能會帶來很多開銷。

有沒有人能成功製作一個很好的Scala Query多對多的實現？

Answer 1

編輯
您可以模擬GROUP_CONCAT像這樣：

val groupConcat = SimpleFunction[String]("GROUP_CONCAT") 

如果您在查詢範圍這種方法，應該就這麼簡單：

yield (alias.a, alias.b, groupConcat(alias.c)) 

因爲我存儲這些輔助函數在抽象數據庫包裝器中執行，並在特定的DBMS（如MySQL）中實現，因此它會變得更加複雜，因爲SimpleFunction類型簽名需要此抽象方法defin銀行足球比賽：

val groupConcat: (Seq[Column[_]] => OperatorColumn[String]) 

這意味着實現需要一個在SEQ（alias.c），這是一個有點直覺相反，我們只是傳遞一個單列通過。無論如何，愉快地工作，GROUP_CONCAT是在MySQL

ORIGINAL相當方便
神知無不言，發佈您的代碼什麼是錯的，但試試這個：

val q = (for { 
    tp <- TagPost 
    p <- Post if tp.post_id is p.id 
    t <- Tag if tp.tag_id is t.id 
    _ <- Query groupBy p.id 
} yield (p.id, p.content, p.posted_date, group_concat(t.name))) 
println(q.selectStatement) 

你將需要創建一個函數來複制MySQL的GROUP_CONCAT。見SimpleFunction source;這個對象的一元方法允許你將一個命名列傳遞給底層的DBMS函數。

val group_concat = 
    SimpleFunction.unary[NamedColumn[String], String]("GROUP_CONCAT") 

Answer 2

我終於完成了該方法。
不幸的是它是供應商特定的。

def allPosts = database.withSession { implicit db: Session => 
    val group_concat_string_tmp = SimpleFunction[String]("GROUP_CONCAT") 
    def group_concat_string(c: Column[String]) = group_concat_string_tmp(Seq(c)) 
    def group_concat_long(c: Column[Long]) = group_concat_string_tmp(Seq(c)) 
    val query = for{ 
     tp <- TagPostTable 
     tag <- TagTable if tp.tag_id is tag.id 
     post <- PostTable if tp.post_id is post.id 
     _ <- Query groupBy post.id 
    } yield post.id ~ post.content ~ post.postedDate ~ group_concat_long(tag.id) ~ group_concat_string(tag.name) 
    println(query.selectStatement) 
    def parseToTagList(ids: String, names: String) : List[Tag] = { 
     (ids.split(',') map (_.toLong) , names.split(',')).zipped map (Tag(_,_)) toList 
    } 
    query.list map (queryResult => Post(queryResult._1, queryResult._2, queryResult._3, Option(parseToTagList(queryResult._4, queryResult._5)))) 
    } 

而生成的SQL查詢是奇異:) YES！

SELECT `t1`.`id`,`t1`.`content`,`t1`.`posted_date`,GROUP_CONCAT(`t2`.`id`),GROUP_CONCAT(`t2`.`name`) 
FROM `tag_post` `t3`,`post` `t1`,`tag` `t2` 
WHERE (`t3`.`tag_id`=`t2`.`id`) AND (`t3`.`post_id`=`t1`.`id`) 
GROUP BY `t1`.`id`