database error handling

commandonz

I'm nearing completion of my first php development, and i'm starting to put error handling in place. Right now my error handling is like this

$result = mysql_query($query, getDbConnection()) or die("getImages select Failed!");

which means the user just sees a short and not at all helpful message if the database query fails. They shouldn't fail that often, but I have some reasonably complex SQL, there's a chance that the odd one could fail until the systems been shaken down.

Does anyone have a pattern for showing a nicer error page when something goes wrong? Right now what i'm thinking of doing is something like this:

$ERROR = (a constant of some kind);

function doDatabaseStuff() {
$result = mysql_query($query, getDbConnection());
if (!$result) {
  return $ERROR;
}

$res = doDatabaseStuff();
if ($res == $ERROR) {
  smarty->include("errorPage.tpl");
}

Would anyone care to comment on this before I get started on it? It's easy to change all my mysql code, they're all inside functions in 1-2 php scripts.

I must get around to adding logging soon too.

TIA for any ideas 🙂

devinemke

my general approach is this:

-header
-middle (where all of the page specific content is)
-footer

these are typically slung together using includes. there may of course be database related content in the header and footer but rather than halt the whole page i usually just output a blank space where that content would be if the database is unavilable.

the middle is different. if an error occurs during the middle section then i: trap the error, spit out a meaningful error message to the user, display the footer, then exit:

if (!$db_connect)
{
	echo 'our database is currently down.  please check back later';
	include('footer.php');
	exit();
}

this way you don't have to have complex nested if conditional logic in your middle code, you can simply call exit where needed. obviously the trick is to call include('footer.php') before calling exit() so all of your HTML is closed out nicely (...</table></body></html>). i sometimes devise my own error code system (db_fail, mail_fail, etc...) and either write this to a log file or display this code in the error message so users can see what's going on.