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Databases
Best Practices: Database Abstraction - Page 4
by: Allan Kent
|
January 15, 2001
What about error checking ?
Say we ran the MySQL script again, and made a bit of a typo in the SQL statement -
$sql = "SELECT * FROM demo2";
Warning: Supplied argument is not a valid MySQL result resource in c:\temp\allan\db\mysql.php on line 7
Messy. So we could add some error checking to the line that does the query:
$demoResult = mysql_query( $sql ) or die( $sql );
which now will output
SELECT * FROM demo2
Which means we have an error and we can go and debug it. Course if you've got a couple of inner joins happening you may not easily be able to work it out. And if I made a typo in one of the field names I was selecting:
$sql = "SELECT bogus_field FROM demo";
I would get the same error message.
MySQL has a useful function called
mysql_error() which will return the last error that was generated, so
changing the line:$demoResult = mysql_query( $sql ) or die( $sql );
to
$demoResult = mysql_query( $sql ) or die( mysql_error() );
will now result in
Table 'phptst.demo2' doesn't exist
in the first case and
Unknown column 'bogus_field' in 'field list'
in the second.
So what does PEAR have to offer in the way of error reporting ?
The function
DB::isError() will check to see whether the result that has been returned to you is an error or not. If it is an error you can use DB::errorMessage() to return a text description of the error that was generated. You need to pass DB::errorMessage() the return value from your function as an argument.
Rewriting the PEAR code to use the error checking:
<?php
if ( DB::isError( $demoResult = $db->query( $sql ) ) ) {
echo DB::errorMessage($demoResult);
} else {
while ($demoRow = $demoResult->fetchRow()) {
echo $demoRow[2] . '<br>';
}
}
?>
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