Scala 在slick中更新表的前n行
使用Scala 在slick中更新表的前n行,scala,slick-3.0,Scala,Slick 3.0,使用slick 3.0时,我想更新表的前n行,而不是整个行 这是“全部更新”版本: private[this] val active = this.filter(a => a.status =!= AccountStatus.DISABLED) db.run( active.filter(a => a.usedBy.isEmpty || a.usedBy === Host.name) .map(account => account.usedBy) .up
slick 3.0时,我想更新表的前n行,而不是整个行
这是“全部更新”版本:
private[this] val active = this.filter(a => a.status =!= AccountStatus.DISABLED)
db.run(
active.filter(a => a.usedBy.isEmpty || a.usedBy === Host.name)
.map(account => account.usedBy)
.update("host-a")
)
我试图使用这个版本,但它不起作用,并抛出了一个异常
private[this] val active = this.filter(a => a.status =!= AccountStatus.DISABLED)
db.run(
active.filter(a => a.usedBy.isEmpty || a.usedBy === Host.name)
.take(10)
.map(account => account.usedBy)
.update(Option(Host.name))
)
例外情况
Caused by: slick.SlickException: A query for an UPDATE statement must resolve to a comprehension with a single table -- Unsupported shape: Comprehension s2, Some(Apply Function and), None, ConstArray(), None, None, Some(LiteralNode 100 (volatileHint=false)), None
at slick.driver.JdbcStatementBuilderComponent$QueryBuilder.buildUpdate(JdbcStatementBuilderComponent.scala:447)
at slick.driver.JdbcProfile$$anonfun$updateCompiler$1.apply(JdbcProfile.scala:30)
at slick.driver.JdbcProfile$$anonfun$updateCompiler$1.apply(JdbcProfile.scala:30)
at slick.jdbc.JdbcMappingCompilerComponent$JdbcCodeGen.compileServerSideAndMapping(JdbcMappingCompilerComponent.scala:59)
嗯。。。这个问题的答案在于,你正试图做一些斯里克不应该做的事情
一个非常简单的指导原则-当有疑问时,用SQL思考,然后转换为Slick
试想一下,您将如何在SQL中实现这一点
如果我转换你的“查询”
对于SQL,它将是这样的
UPDATE
active
SET
used_by = 'Awesome-Host'
WHERE
used_by IS NULL
OR used_by = 'Awesome-Host'
LIMIT 10
从SQL的角度来看这有点荒谬
现在。。。让我们讨论一下如何使用SQL实际执行此操作
UPDATE
(
SELECT
*
FROM
active
WHERE
used_by IS NULL
OR used_by = 'Awesome-Host'
LIMIT 10
) active_selection
SET
active_selection.used_by = 'Awesome-Host'
而且。。。可以使用子查询将其转换为Slick
val activeSelection = active
.filter(a => a.usedBy.isEmpty || a.usedBy === Host.name)
.take(10)
val updateSelection = activeSelection
.map(a => a.usedBy)
.update(Option(Host.name))
课程->如果你不能用SQL做一些事情,那么你就不能用Slick做这些事情。@SarveshKumarSingh哦,你可以用SQL轻松地做到这一点。你为什么这么说?谢谢@Singh,但是第一个SQL转换应该与MySQL一起使用。我使用MySQL。但是,我会尝试第二种情况,看看它是否有效,并让你知道。
val activeSelection = active
.filter(a => a.usedBy.isEmpty || a.usedBy === Host.name)
.take(10)
val updateSelection = activeSelection
.map(a => a.usedBy)
.update(Option(Host.name))