找不到带有Scala编解码器的Datastax Cassandra驱动程序

Question

1. DataStax驱动程序Cassandra版本:3.3.2
2. Scala版本:2.12.4

我正在为Cassandra的datastax java驱动程序中的mappingmanager创建一个scala包装器。

CREATE TABLE todo (
    id UUID,
    title TEXT,
    completed boolean,
    PRIMARY KEY((id), completed, title)
)  WITH CLUSTERING ORDER BY (completed ASC, title ASC);

private def executeAsync(query: String, params: Any*): Future[ResultSet] = {
    params match {
      case Seq() =>
        session.executeAsync(query) // had a problem with empty params varargs
      case _ =>
        prepareAsync(query).map(preparedStatement =>
          preparedStatement.bind(
            params
              .map(x => {
                println(x) // correctly prints the param
                x.asInstanceOf[Object]
              })
          )
        ).flatMap(x => {
          println("here") // never gets printed
          session.executeAsync(x)
        })
    }
  }

  private def prepareAsync(query: String): Future[PreparedStatement] = {
    session.prepareAsync(query)
  }

val future: Future[List[TodoCassandra]] = customMappingManager.executeQueryAsync("SELECT * FROM todo;")
    future.onComplete {
      case Success(x) =>
        println(x)
    }

val future: Future[List[TodoCassandra]] = customMappingManager.executeQueryAsync("INSERT INTO todo (id, title, completed) VALUES (uuid(), ?, ?)", "prepared statement test", false)

val future: Future[List[TodoCassandra]] = customMappingManager.executeQueryAsync("INSERT INTO todo (id, completed, title) VALUES (uuid(), ?, ?)", false, "prepared statement test")

val future: Future[List[TodoCassandra]] = customMappingManager.executeQueryAsync("SELECT * FROM todo WHERE id = ?", "a8a6da8b-3d0e-40b3-99e5-fe2f664f50d0")

null

为什么它总是从Scala.Collection.Mutable.ArrayBuffer“转换”？解决这个问题的方法是什么？

Answer 1

在使用从Scala教程查询Cassandra时，我遇到了与您类似的问题。

您的executeAsync方法与本文中的方法类似，并且具有相同的缺陷。也就是说，在PreparedStatement.bind期间，在将每个any项强制转换为Object之后，您传递一个seq[Object]。而这似乎失败了。

简单的解决方法是，按照Java方法的实际要求，将该序列作为var-args传递。

代码：

def execute(statement: Future[PreparedStatement], params: Any*)
           (implicit executionContext: ExecutionContext, session: Session): Future[ResultSet] = {
  val p = params.map(_.asInstanceOf[Object])
  statement
    .map(_.bind(p: _*))
    .flatMap(session.executeAsync(_))
}