但是我想知道,在下面的代码中,我如何检查一个表是否存在,所以我不会调用“Table.ddl.create”两次,当我运行这个程序两次得到一个异常？

object Users extends Table[(Int,String,String)]("Users") {
    def id = column[Int]("id")
    def first = column[String]("first")
    def last = column[String]("last")
    def * = id ~ first ~ last
}

object Main
{
    val database = Database.forURL("jdbc:sqlite:sample.db",driver = "org.sqlite.JDBC")

    def main(args: Array[String]) {
        database withSession {
            // How could I know table Users is alrady in the DB?
            if ( ??? )  {
                Users.ddl.create
            }
        }
    }
}