php exceptions extra parameters

Question

Is it possible to add an extra parameter when throwing an exception?

When I throw an exception I send along the error message but I would also like to send along the name of the field in a extra parameter. Something like:

throw new Exception('this is an error message', 'the field');

So when I display the message I can do something like this:

show_error($e->getFieldname, $e->getMessage());

Answer 1

No, you would have to subclass Exception with your own implementation and add that method.

class FieldException extends Exception
{
    protected $_field;
    public function __construct($message="", $code=0 , Exception $previous=NULL, $field = NULL)
    {
        $this->_field = $field;
        parent::__construct($message, $code, $previous);
    }
    public function getField()
    {
        return $this->_field;
    }
}

But actually, I am not a friend of adding methods or properties to Exceptions. An Exception represents just that: something exceptional that happened in your application. The "field" property is really not part of the Exception, but part of the exception message, so I'd probably use a proper message like:

Wrong value for field foo. Excepted string, got integer

Answer 2

There is no need to add an extra parameter.

You can just throw an Exception like this:

throw new Exception("My Exception Text", 1234);

And access both values:

catch (Throwable $t)
{  
    echo var_dump($t);
    echo "Exception: " . $t->getMessage();
    echo "Code: " . $t->getCode();
}

Answer 3

What I do, is have a class to create custom exceptions, but to standardise matters, I simply have one additional argument, which is an object (well, so far it's always been an array), which allows me to specify unlimited amount of exception data (much like a javascript exception).

Output:

Fatal error: Uncaught SqlProxyException 'Duplicate entry '1' for key 'PRIMARY'' in     /usr/src/wrangler/trunk/common/SqlProxy.php(356)
#0 /usr/src/wrangler/trunk/common/SqlProxy.php(341): SqlProxy::Update('INSERT into tes...')
#1 /usr/src/wrangler/trunk/common/SqlProxy.php(455): SqlProxy::Insert('INSERT into tes...')
#2 {main}
Array
(
[sql] => INSERT into test SET test='1'
[errorObject] => Array
    (
        [status] => UNKNOWN
        [data] => Array
            (
                [rowsAffected] => -1
                [errorMsg] => Duplicate entry '1' for key 'PRIMARY'
                [errorCode] => 1062
....

This is achieved by the following in my code:

<? require_once "CustomException.php";

## Define the custom exception
class SqlProxyException extends CustomException {}

## Throw a custom exception
throw new SqlProxyException($errorMsg, $errorCode, null, 
    array("sql" => $query, "errorObject" => $result)
);

## Catch the custom exception

try {
   SqlProxy::Insert($argv[2]);
} catch (SqlProxyException $e) {
   fprintf(STDERR, "Fatal error: Uncaught SqlProxyException '%s' in %s(%s)\n%s\n%s\n",
       $e->getMessage(), $e->getFile(), $e->getLine(),
       $e->getTraceAsString(),
       $e->getObject() ? print_r($e->getObject(), 1) : ""
   );
   exit(1);
}  

Not too difficult... and the magic behind CustomException.php is

<?php

interface IException
{
    /* Protected methods inherited from Exception class */
    public function getMessage();                 // Exception message
    public function getCode();                    // User-defined Exception code
    public function getFile();                    // Source filename
    public function getLine();                    // Source line
    public function getTrace();                   // An array of the backtrace()
    public function getTraceAsString();           // Formated string of trace

    /* Overrideable methods inherited from Exception class */
    public function __toString();                 // formated string for display
    public function __construct($message = null, $code = 0);

}

abstract class CustomException extends Exception implements IException
{ 
    protected $message = 'Unknown exception';     // Exception message
    private   $string;                            // Unknown
    protected $code    = 0;                       // User-defined exception code
    protected $file;                              // Source filename of exception
    protected $line;                              // Source line of exception
    protected $object = null;                     // Extra information in an object (array) js style
    private   $trace;                             // Unknown

    public function __construct($message = null, $code = 0, Exception $previous = null, $eventObject = null)
    {
        if (!$message) {
            throw new $this('Unknown '. get_class($this));
        }
       parent::__construct($message, $code, $previous);
       $this->object = $eventObject;
    }

    public function __toString()
    {
        return get_class($this) . " '{$this->message}' in {$this->file}({$this->line})\n"
                                . "{$this->getTraceAsString()}";
    }

   /* Additional custom method */
   public function getObject()                   // Return object (array) of extra info (js style)
   {
      return $this->object;
   }
}

Answer 4

You can implement your own Exception class, and customize it.

See Extending Exceptions article for details.