如何获取表= Rep [Option [Long]]的max（id）进行后续插入，而无需在之间调用db.run [英] How to get max(id) of table = Rep[Option[Long]] for subsequent insert, without calling db.run in between

问题描述

我在一个表中有一个插入，这取决于另一个表的最大ID。

I have an insert to a table, that depends on the max id of another table.

def add(languageCode: String,
      typeId: Long,
      properties: Seq[Property]): Unit = {
        val dbAction = (
            for{
                nodeId <- (nodes.all returning nodes.all.map(_.id)) += Node(typeId)
                language <- (languages.all filter (_.code === languageCode)).result.head
                _ <- DBIO.seq(properties.map
                {
                property =>
                    val id = property.id
                    val name = property.key
                    val value = property.value
                    if(id == 0) {
                      val currentPropId: FixedSqlAction[Option[Long], h2Profile.api.NoStream, Effect.Read] = this.properties.all.map(_.id).max.result
                      val propertyId = (this.properties.all returning this.properties.all.map(_.id)) += Property(language.id.get, currentPropId + 1, name)
                      nodeProperties.all += NodeProperty(nodeId, 2, value)
                    } else {
                      nodeProperties.all += NodeProperty(nodeId, id, value)
                    }
                }: _*)
            } yield()).transactionally

            db.run(dbAction)
}

您可以看到，问题在于 currentPropId 的类型为 Rep [Option [Long]] ，当然，属性需要一个正确的 Long 代替。

As you can see, the problem is that currentPropId is of type Rep[Option[Long]] and of course Property needs a proper Long instead.

对于languageId，足以添加结果到查询（languages.all过滤器（_.code === languageCode））。result.head

For the languageId it sufficed to add a result to the query (languages.all filter (_.code === languageCode)).result.head

但是对于 currentPropId 而言，类型仍然是 FixedSqlAction

But for the currentPropId the type then still is of FixedSqlAction

编辑：

以这种方式尝试

if(id == 0) {
    this.properties.all.map(_.id).max.map {
        id =>
            val propertyId = (this.properties.all returning this.properties.all.map(_.id)) += Property(language.id.get, id+1, name)
            val nodeProperty = nodeProperties.all += NodeProperty(nodeId, 2, value)

            propertyId andThen nodeProperty
}

不起作用，因为它不再是 Seq [DBIOAction] 而是 Seq [Object] （不是 Any ，而是 Object ）

Does not work, because that's not a Seq[DBIOAction] anymore but a Seq[Object] (Not Any, but Object)

推荐答案

您不能将提升类型（Rep [_]）与标准Scala类型混合使用。
您可以映射到 SqlAction 以提取所需的类型。

You cannot mix the lifted types (Rep[_]) with standard Scala types. You can map over your SqlAction to extract the needed type.

val currentPropId: FixedSqlAction[Option[Long], NoStream, Effect.Read] = ???
currentPropId.flatMap { id: Option[Long] =>
  ???
}

在您的情况下，类似这样：

In your exact case, something like this:

if(id == 0) {
  properties.map(_.id).max.result.flatMap { id: Option[Long] =>
    val propertyId = (properties returning properties.map(_.id)) += Property(language.id.get, id.map(_ + 1), name)
    val nodeProperty = nodeProperties += NodeProperty(nodeId, 2, value)

    propertyId andThen nodeProperty
  }
}
...

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