Question

我有一个我在Scala中编写的ETL框架，并且为每个SQL查询和我执行的更新删除相同的try / catch和closing语句的名称，我做了这个特性，我混合到我的所有SQL连接。 / p>

trait SqlConnection {

  private val defaultHandling = (stmt: PreparedStatement) => stmt.executeUpdate()
  protected val con: java.sql.Connection

  final def executeSimpleUpdate(sql: String): Unit = executeUpdate(sql)(defaultHandling)

  final def executeUpdate[T](sql: String)(statementHandling: PreparedStatement => T) = {
    val stmt = con.prepareStatement(sql)
    try { statementHandling(stmt) } finally { if (!stmt.isClosed) stmt.close() }
  }

  final def executeQuery[T](sql: String)(resultHandling: ResultSet => T) = {
    val stmt = con.prepareStatement(sql)
    try {
      val rs = stmt.executeQuery()
      try { resultHandling(rs) } finally { if (!rs.isClosed) rs.close() }
    } finally { if (!stmt.isClosed) stmt.close() }
  }

  final def close() = con.close()

}

但是，当我运行它时，没有任何命令被执行。我添加了println来尝试隔离哪些行或代码没有运行，这给了我这个错误。

Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.Util.getInstance(Util.java:386)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
    at com.mysql.jdbc.ConnectionImpl.throwConnectionClosedException(ConnectionImpl.java:1320)
    at com.mysql.jdbc.ConnectionImpl.checkClosed(ConnectionImpl.java:1312)
    at com.mysql.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:4547)
    at com.mysql.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:4512)
    at util.SqlConnection$class.executeQuery(Connection.scala:50)

我认为我的问题是误解了Scala如何处理函数值以及何时执行函数。

任何人都可以解释这里发生的事情或者类似的解决方案是什么吗？也许使用内联？

Answer 1

不要将您的连接保持为班级中的字段。将数据库操作包装在一个为您打开和关闭连接的函数中。试试这个：

private def withConnection[A](f: Connection => A): A = {
   val con = JDBC.giveMeAConnection()// Do whatever you want to open a connection
   val result = f(con)
   con.close()
   result
}

final def executeQuery[T](sql: String)(resultHandling: ResultSet => T) = withConnection { conn =>
   // Use conn as you wish here.
}

Scala curried函数似乎不适用于JDBC连接

1 个答案: