问题
I am using nscala-time (wrapper for Joda Time) and slick for a project. I'm trying to use this clause to write a line to the database:
Article.insert(0,"title1", "hellothere", DateTime.now.getMillis.asInstanceOf[Timestamp])
Apparently Slick does not support "dateTime" type defined in Joda Time, and I have to use java.sql.Timestamp instead. So I decide to do a little conversion inside the insert method, using "asInstanceOf". Unfortunately, Scala quickly tells me that Java.Long cannot be converted to Java.sql.Timestamp. Then I used this:
val dateTime = new DateTime();
val timeStamp = new Timestamp(dateTime.getMillis());
Article.insert(0,"title1", "hellothere", timeStamp)
This magically works, and all I'm left with is confusion.
How can I convert it one way but not the other? Should I use a different conversion than asInstanceOf?
回答1:
You misunderstand what asInstanceOf does: asInstanceOf doesn't convert anything. What it does is lie to the compiler, telling it to believe something instead of going with the knowledge it has.
So, you had a Long, and then you got a Long, but pretended it was a Timestamp, which obviously doesn't work.
I have a simple recommendation regarding asInstanceOf: never use it.
回答2:
There's no magic about it. Your first statement:
DateTime.now.getMillis
is a Long. A Long is not a Timestamp, so it makes sense that you can't convert it to one by using asInstanceOf.
The second statement:
new Timestamp(dateTime.getMillis())
is using the Timestamp constructor to create a new Timestamp instance based on the dateTime.getMillis.
来源：https://stackoverflow.com/questions/20663662/scala-conversion-long-to-datetime