Re: [PHP] Class Design Question...

On Wed, 6 Aug 2003 11:33:54 -0500, you wrote:

>Basically in the class I have methods that perform a task, and return true
>on success, or false on failure. Easy enough. If it returns false however, I
>want to display errors for the user. The best way I can think of doing this
>is adding a member variable to the class (an array). With each error
>encountered it would push them on the array and at the end of the function
>return false. Then in the code I would check if it returned false, and if so
>dive into the error member variable array of the class and display them...

That's pretty much the approach I use. It allows me to produce something
like a stack trace...

"Error: Can't connect to database in _runQuery() in _userExists() in
createUser()", style of fing.

I tried including a generic error object within the class, but it just adds
a level of indirection for very little benefit. Now I just have a $error
variable in every class, and a _setError() function to manipulate it (make
sure you set $error to false in the constructor, of course). This is from my
database class, hence the mysql_errno() catch.

/* add $s to the error string, and return false */
function _setError ($f, $l, $e = FALSE)
{
if ($this->error === FALSE)
{
if ($m = @mysql_errno($this->_dbconn))
{
$m = "($m)";
}
$s = "Error: $e $m on line $l in function Database->$f()";
} else {
$s = ", on line $l in function Database->$f()";
}
$this->error = $this->error . $s;
return (FALSE);
}

which can be called like this:

if (!is_int ($max))
{
return ($this->_setError (__FUNCTION__, __LINE__, "invalid data '$max'"));
}

or like this

if ($this->error)
{
return ($this->_setError (__FUNCTION__, __LINE__));
}

>This sound like good design? Any suggestions?

Whether it's good design or not... not particularly. But it's probably the
best you'll get without support for exceptions.

I should add that testing the error string makes more sense than testing the
return value of the function. Lets say you have a function that tests
whether a given user exists. It returns userid if the user is found, else
FALSE. How do you tell the difference between user-not-found and
database-crashed?

if (($userid = $db->userExists ($username)) == FALSE)
{
if ($db->error)
{
/* there was an error */
die ($db->error);
} else {
/* user was not found */
$db->createUser ($username);
}
} else {
/* user found */
echo ($userid);
}