我想在使用时更新表的前 n 行而不是整个行slick 3.0
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，但它不起作用并引发异常
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
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
试想一下如何在 SQL 中实现这一目标，
如果我改变你的“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，它会是这样的，
UPDATE
active
SET
used_by = 'Awesome-Host'
WHERE
used_by IS NULL
OR used_by = 'Awesome-Host'
LIMIT 10
从 SQL 的角度来看，这有点荒谬......
现在...让我们谈谈如何使用 SQL 实际做到这一点，
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......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))
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