correct way of using a throw try catch error handling

Question

I have come accross to this function below and I am wondering wether this is the right way of using the error handling of try/catch.

public function execute()
{
    $lbReturn = false;
    $lsQuery = $this->msLastQuery;
    try
    {
        $lrResource = mysql_query($lsQuery);

        if(!$lrResource)
        {
            throw new MysqlException("Unable to execute query: ".$lsQuery);
        }
        else
        {
            $this->mrQueryResource = $lrResource;
            $lbReturn = true;
        }

    }
    catch(MysqlException $errorMsg)
    {
        ErrorHandler::handleException($errorMsg);
    }
    return $lbReturn;
}

Looking at the code, I would say that the author of this function only threw the exception so that he could log it using an already existing logging functionality. — Mladen Mihajlovic
– Mladen Mihajlovic, Commented Apr 19, 2009 at 10:34

Bob Fanger · Accepted Answer · 2009-04-19 15:31:01Z

5

Codewise it is correct/works, However the power of try-catch is that when an Exception is thrown from deep down in one of the functions you're calling.
Because of the "stop execution mid-function and jump all the way back to the catch block".

In this case there are no deep-down exceptions therefore I would write it like this:
(Assuming there is a function "handleErrorMessage" in the ErrorHandler.)

public function execute() {
    $lsQuery = $this->msLastQuery;
    $lrResource = mysql_query($lsQuery);

    if(!$lrResource) {
         ErrorHandler::handleErrorMessage("Unable to execute query: ".$lsQuery);
         return false;
    }
    $this->mrQueryResource = $lrResource;
    return true;
}

Which I find more readable.

edited Apr 19, 2009 at 15:31

answered Apr 19, 2009 at 10:42

Bob Fanger

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2 Comments

sanders Over a year ago

Thanks for your commment. What would be if I would replace ErrorHandler::handleErrorMessage($errorMsg); with the throw statement? Would that be incorrect?

Bob Fanger Over a year ago

That would cause the function execute() to be aborted and jump to a catch block(if any) outside of the execute function. Which dramatically changes the behaviour of the function. If this new behaviour is "incorrect" is up to you.

pauljwilliams · Accepted Answer · 2009-04-19 10:10:45Z

5

No. Throwing an exception in this case is simply a GOTO, but with a (slightly) prettier face.

answered Apr 19, 2009 at 10:10

pauljwilliams

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Comments

Robin Barnes · Accepted Answer · 2009-04-19 16:14:51Z

1

Why have a call to ErrorHandler::handleException here anyway?

Just throw the exception, but never catch it. Then in the global initialization code for your app have a function with the following signature:

function catchAllExceptions(Exception $e)

Then call:

set_exception_handler('catchAllExceptions');

This will cause all uncaught excpetions to be passed as an argument to catchAllExceptions(). Handling all uncaught exceptions in one place like this is good, as you reduce code replication.

answered Apr 19, 2009 at 16:14

Robin Barnes

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Comments

BYK · Accepted Answer · 2009-04-19 10:32:41Z

0

Well it is not really a good implementation since you throw the exception and you look for that exception in catch. So the answer of Visage is true.

You should use a global error handler instead of a tr-catch usage like in your code.
If you are not sure of the type of the error and occurance but want to continue the execution of the code although an exception had occured, then a try-catch block will help.

answered Apr 19, 2009 at 10:32

BYK

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