How to "throw" a %Status to %ETN? - intersystems-cache

Question

Many of the Caché API methods return a %Status object which indicates if this is an error. The thing is, when it's an unknown error I don't know how to handle (like a network failure) what I really want to do is "throw" the error so my code stops what it's doing and the error gets caught by some higher level error handler (and/or the built-in %ETN error log).
I could use ztrap like:
s status = someObject.someMethod()
ztrap:$$$ISERR(status)
But that doesn't report much detail (unlike, say, .NET where I can throw an exception all the way to to the top of the stack) and I'm wondering if there are any better ways to do this.

Answer 1

Take a look at the Class Reference for %Exception.StatusException. You can create an exception from your status and throw it to whatever error trap is active at the time (so the flow of control would be the same as your ZTRAP example), like this
set sc = someobj.MethodReturningStatus()
if $$$ISERR(sc) {
set exception = ##class(%Exception.StatusException).CreateFromStatus(sc)
throw exception
}
However, in order to recover the exception information inside the error trap code that catches this exception, the error trap must have been established with try/catch. The older error handlers, $ztrap and $etrap, do not provide you with the exception object and you will only see that you have a <NOCATCH> error as the $ZERROR value. Even in that case, the flow of control will work as you want it to, but without try/catch, you would be no better off than you are with ZTRAP

Answer 2

These are two different error mechanisms and can't be combined in this way. ztrap and %ETN are for Cache level errors (the angle bracket errors like <UNDEFINED>). %Status objects are for application level errors (including errors that occurred through the use of the Cache Class Library) and you can choose how you want to handle them yourself. It's not really meaningful to handle a bad %Status through the Cache error mechanism because no Cache error has occurred.
Generally what most people do is something akin to:
d:$$$ISERR(status) $$$SomeMacroRelevantToMyAppThatWillHandleThisStatus(status)
It is possible to create your own domain with your own whole host of %Status codes with attendant %msg values for your application. Your app might have tried to connect to an FTP server and had a bad password, but that doesn't throw a <DISCONNECT> and there is no reason to investigate the stack, just an application level error that needs to be handled, possibly by asking the user to enter a new password.
It might seem odd that there are these two parallel error mechanisms, but they are describing two different types of errors. Think of one of them being "platform" level errors, and the other as "application level errors"
Edit: One thing I forgot, try DecomposeStatus^%apiOBJ(status) or ##class(%Status).LogicalToOdbc(status) to convert the status object to a human readable string. Also, if you're doing command line debugging or just want to print the readable form to the principal device, you can use $system.OBJ.DisplayError(status).