10.10. Logging Debugging Information and Errors

Problem

You want access to information to help you debug database problems. For example, when a query fails, you want to see what error message the database returns.

Solution

Use DB::isError( ) to investigate the results of a single query:

$sth = $dbh->query("SELECT aroma FROM zodiac WHERE element LIKE 'fire'");
DB::isError($sth) and print 'Database Error: '.$sth->getMessage();

Use DB::setErrorHandling( ) to automatically take action on any database error:

$dbh->setErrorHandling(PEAR_ERROR_PRINT);
$sth = $dbh->query("SELECT aroma FROM zodiac WHERE element LIKE 'fire'");

Discussion

When they encounter an error, most PEAR DB methods return an DB_Error object. The DB::isError( ) method returns true if it’s passed a DB_Error object, so you can use that to test the results of individual queries. The DB_Error class is a subclass of PEAR::Error, so you can use methods such as getMessage( ) to display information about the error. If you want to display everything in the error object, use print_r( ) :

$sth = $dbh->query('SELECT aroma FROM zodiac WHERE element LIKE 'fire'");
if (DB::isError($sth)) {
    print_r($sth);
}

Since there is no aroma column in the zodiac table, this prints:

db_error Object ( [error_message_prefix] => [mode] => 1 [level] => 1024 [code] => -19 [message] => DB Error: no such field [userinfo] => SELECT aroma FROM zodiac WHERE element LIKE 'fire' \ [nativecode=1054 ** Unknown column 'aroma' in 'field list'] [callback] ...

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