我想在使用
slick 3.0
时更新表格的前 n 行而不是整个行
这是更新所有版本:
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")
)
我尝试使用这个版本,但它不起作用并抛出异常
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))
)
异常
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,您正在尝试做一些 Slick 不应该做的事情。
一个非常简单的指南 - 当有疑问时用 SQL 思考,然后转换为 Slick
想一想如何在 SQL 中实现这一目标,
如果我转换你的“查询”,
// lets say Host.name = "Awesome-Host"
active.filter(a => a.usedBy.isEmpty || a.usedBy === Host.name)
.take(10)
.map(account => account.usedBy)
.update(Option(Host.name))
对于SQL来说,会是这样的,
UPDATE
active
SET
used_by = 'Awesome-Host'
WHERE
used_by IS NULL
OR used_by = 'Awesome-Host'
LIMIT 10
从 SQL 角度来看,这有点荒谬......
现在...让我们谈谈如何使用 SQL 来实现它,
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'
并且...这可以使用子查询转换为 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))
我们最近遇到了类似的情况。
解决方案是使用子查询:
val subquery = myTable.filter(...).take(1)
myTable
.filter(_.id in subquery.map(_.id))
.map(row => ...)
.update(...)