User Authentication With patUser (part 3) - Making Exceptions

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First up, error handling. You'll have seen, from the previous sections of this article, that many of patUser's functions return either true or false to indicate success or failure; this value can then be used in your script to display an appropriate status message.

However, patUser also goes further, allowing you to display a more verbose message indicating the cause of error if one occurred. A built-in error stack keeps track of all the errors that have occurred, and the library include a number of functions designed to help you read and modify this stack.

The two functions you're most likely to use are getLastErrorCode() and getLastErrorMessage(), which return the last error code and message respectively. Consider the following example, which demonstrates:

<?php
// include classes
include("../include/patDbc.php"); include("../include/patUser.php");
// initialize database layer
$db = new patMySqlDbc("localhost", "db211", "us111", "secret");
// initialize patUser
$u = new patUser(true);
// connect patUser to database
$u->setAuthDbc($db);
// set tables
$u->setAuthTable("users");
// add user
$u->addUser( array("username" => "tom", "passwd" => "tom") );
// add user again
$u->addUser( array("username" => "tom", "passwd" => "tom") );
// get message and display
echo "Operation failed. " . $u->getLastErrorMessage() . " (#" .
$u->getLastErrorCode() . ")";
?>

Since there's a subtle error in the script above, patUser will not be able to execute the call to addUser() successfully. An error code will be generated internally and added to the error stack; this code can be viewed and retrieved via the calls to getLastErrorCode() and getLastErrorMessage(). Here's an example of what you might see:



Obviously, this is a little more informative than the standard "User could not be added" message.

You can also use the shortcut getLastError() method, which returns an array containing both error code and message. The following example, which is equivalent to the one above, illustrates:

<?php
// include classes
include("../include/patDbc.php"); include("../include/patUser.php");
// initialize database layer
$db = new patMySqlDbc("localhost", "db211", "us111", "secret");
// initialize patUser
$u = new patUser(true);
// connect patUser to database
$u->setAuthDbc($db);
// set tables
$u->setAuthTable("users");
// add user
$u->addUser( array("username" => "tom", "passwd" => "tom") );
// add user again
$u->addUser( array("username" => "tom", "passwd" => "tom") );
// get message and display
$e = $u->getLastError();
echo "Operation failed. " . $e['message'] . " (#" .  $e['code'] . ")";
?>

You can obtain a complete list of all the errors in the stack via the getAllErrorCodes() and getAllErrorMessages() methods, which return arrays of all the error codes and messages generated by patUser during the execution of the script, or again use the equivalent shortcut method getAllErrors() to get both codes and messages in one pass. A complete list of possible error codes and what they mean is available in the patUser documentation.

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