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Appropriate use of exceptions

Posted on 2007-12-01
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Last Modified: 2013-12-13
I can best present this question with code...

Thanks
//This is how you'd (presumably) normally work with exceptions...
 
//within the class
public function query($query) {
 if (!$query = @mysql_query($query,$this->conn)) {
  throw new Exception('Query Error');
 }
 return $query;
}
 
//code
$db = new classname();
try {
 $db->query('the_query'); 
}
catch (Exception $e) {
 die($e->getMessage());
}
 
#########################################
 
/* but I'm thinking as an exception thrown will always result in the
 termination of the script here, and I'd otherwise have to include
 the try-catch block every time I want to run a query; would it not 
make more sense to just build it into the class? i.e. */
 
#########################################
 
//within the class
public function query($query) {
 try {
  if (!$query = @mysql_query($query,$this->conn)) {
   throw new Exception('Query Error');
  }
 } catch (Exception $e) {
  die($e->getMessage());
 }
 $this->query_count++;
 return $query;
}
 
//code
$db = new classname();
$db->query('the_query');
 
 
/* is there any reason why this would be considered bad 
practice, or a bad idea? */

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Question by:calcanus
4 Comments
 
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Accepted Solution

by:
Zyloch earned 125 total points
ID: 20388704
If you are just going to kill the script, then you would do it within the function itself, but most of the time, you wouldn't want to be that extreme. You would want some way to notify the calling function that something went wrong. In this case, you would throw your exception. Perhaps, you would log the error to a log file before that inside your function.

Yes, it litters your code with many try-catch clauses. However, since you can pass any message string in an exception, you can use a central catch clause. Or if the function that is catching the exception is part of another function, you can translate multiple exception types into a single exception that is more general (perhaps logging along the way).

That said, you may be able to use set_exception_handler() to handle truly redundant cases.
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LVL 19

Assisted Solution

by:SteveH_UK
SteveH_UK earned 125 total points
ID: 20389160
In this particular case, you might also consider supporting both options by an optional parameter.  That way your code is reusable, and supports informing the caller of an "exceptional" circumstance, but also allows you to choose a default behaviour of exiting your script.
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LVL 16

Expert Comment

by:CWS (haripriya)
ID: 21188508
No comment has been added to this question in more than 21 days, so it is now classified as abandoned.

I will leave the following recommendation for this question in the Cleanup topic area:
   Split: steelseth12 {http:#20388704} & SteveH_UK {http:#20389160}

Any objections should be posted here in the next 4 days. After that time, the question will be closed.

cyberwebservice
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Expert Comment

by:Computer101
ID: 21216914
Forced accept.

Computer101
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