A little help with an if/else mysqli instruction

[schwim2]

Hi there everyone!

I've gotten into the habit of using a numerical id in my query results so if there's an error of any sort, it doesn't give away any information but spits out a numerical string that I can later search the files for to find the issue.

So my result string looks like this:

	$r_linkexist = mysqli_query($link, $q_linkexist) or die('Catastrophic failure [Error code: 8959412]');

and if someone reports it, I search my files for that number, then change the result to print the mysqli_error to find out what the problem is.

What I'd like to do though is have the result automatically show me the error, otherwise print the error code. I tried a bunch of methods but I can only really get this lotso code to do it:

$sqlerror_id = '4787208';
if($viewing_user == '1'){
	$r_topics = mysqli_query($link, $q_topics) or die(mysqli_error($link).'<br><hr><br>'.$q_topics);
}else{
	$r_topics = mysqli_query($link, $q_topics) or die('Catastrophic failure [Error code: '.$sqlerror_id.']');
}

Which leaves me changing a lot of info as I reuse my code elsewhere in the page but I tried less verbose methods, which all failed. Something like:

$sqlerror_id = '4787208' && $sqlerror = 'mysqli_error($sql.'<br><hr><br>'.$q_topics)'; if($viewing_user != '1'){$sqlerror = 'Error code: '.$sqlerror_id);}
$r_topics = mysqli_query($link, $q_topics) or die($sqlerror);

I'm just wondering if any of the people who actually know what in the hell they're doing might be able to give me a minimal snippet that would do this but allow me to reuse with the least amount of modification with other queries.

Thanks for your time!

[Weedpacket]

Consider writing a function to hold all the duplicate stuff.

$r_linkexist = mysqli_query($link, $q_linkexist) or choke("8959412");

[pbismad]

If you use exceptions, you won't need code at each database statement to handle errors. They will throw an exception that you can catch and handle in one place, at the end of your database dependent code.

The exception catch block logic would get the error information (error message, file name where the error occurred, and line number of the statement that triggered the error) and use trigger_error() to either log or display this information. Trigger_error() uses php's error_reporting and display_errors/log_errors settings to control what happens with the information you pass to it, so you would simply display errors when developing or debugging code, and log errors otherwise by just changing the php settings. You would also setup and display a generic message to the visitor, that the site isn't working. The visitor needs no other information, since all the actual error information will be logged.

[Weedpacket]

Also, just calling [man]die[/man] is an ugly way to handle an error.

The MySQLi object carries a bunch of properties that describe its current error state. Should you make your own exception class for this then you could pass the connection object as one of its constructor parameters (along with your made-up error number for user reporting). Then you'll have access to not only PHP's record of where the error occurred and what it was doing at the time, but also MySQL's information about the nature of the error.

[schwim2]

Weedpacket;11062339 wrote:

Also, just calling [man]die[/man] is an ugly way to handle an error.

The MySQLi object carries a bunch of properties that describe its current error state. Should you make your own exception class for this then you could pass the connection object as one of its constructor parameters (along with your made-up error number for user reporting). Then you'll have access to not only PHP's record of where the error occurred and what it was doing at the time, but also MySQL's information about the nature of the error.

Hi there Weedpacket,

Are you saying to pass the connection($sql) into the function so I can take information from it? What would be an example of how I might handle it rather than die?

[schwim2]

I've read up a bit on exceptions and I'm trying to integrate that into a function to handle the error stuff but I'm having a problem with my $link. Even passing it as a global, I don't seem to be able to get the important $link information inside the function. Am I handling it incorrectly?

Here's what I've got thus far:

function sql_blooper($code, $link){

global $viewing_user_id, $link;

if ($link->error) {

	if($viewing_user_id == '2'){

		try {    
			throw new Exception("MySQL error $mysqli->error <br> Query:<br> $q_topics", $msqli->errno);    
		} catch(Exception $e ) {
			echo "Error No: ".$e->getCode(). " - ". $e->getMessage() . "<br >";
			echo nl2br($e->getTraceAsString());
		}
		exit;
	}else{
		echo 'Catastrophic failure [Super secret code '.$code.']';
		exit;
	}
}
}

$query_stuff

$sqlerror_id = '4787208';
$r_topics = mysqli_query($link, $q_topics); sql_blooper($sqlerror_id, $link);

Which is resulting in a mysql error of 0 with no query being printed. If I move this outside of the function and add it behind the result, it does print all the information I'm looking for.

What do I need to change to make this work?

[pbismad]

If you are trying to implement what I wrote, it's the mysqli statements that throw an exception when an error occurs. All you have to do is enable exceptions for the mysqli statements, catch the mysqli exception, and do something with the error information.

<?php

// set mysqli driver error mode to exceptions
$driver = new mysqli_driver();
$driver->report_mode = MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT; // MYSQLI_REPORT_ALL <-- w/index checking; w/o index checking --> MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT;

// start of database dependent code
try {

// make your database connection - needs no error handling logic as this will throw an exception if the connection fails
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");

// the rest of your database dependent code goes within this try {} block

// if you need to handle a specific error, such as a duplicate key/value error, you would put a local try/catch block around the code executing the query in question. if the error isn't one that the local try/catch block is designed to handle, you would re-throw the msyqli_sql_exception so the main try/catch block will handle it.


// end of database dependent code
} catch (mysqli_sql_exception $e) {

echo 'Sorry, the site is not working at this time.'; // output a user message
// get the error information and produce the message you want from it.
$message = "db error: {$e->getmessage()}, File: {$e->getfile()}, Line: {$e->getline()},"; // note: trigger_error() will add the file and line number of the trigger_error() statement to the end of the message.
// you can also use debug_backtrace() to get more information about where the error started at, if you are calling a generic query method/function from multiple places to execute queries
trigger_error($message, E_USER_ERROR); // note: E_USER_ERROR halts program execution
}

// The rest of your code.

Because the message you produce in the error handling contains the file name and line number where the error occurred at, there's no need to use any self-made error numbers because you won't need them to identify where the error occurred at.

[schwim2]

Hi there pbismad, are you saying that instead of using this type of code at the end of every query, I should just run it at the end of the file? Wouldn't that possibly start a chain of failures that would make it harder to track down the root error? I thought that was the benefit of killing the script immediately upon the error.

[laserlight]

schwim2 wrote:

Wouldn't that possibly start a chain of failures that would make it harder to track down the root error? I thought that was the benefit of killing the script immediately upon the error.

Once an exception is thrown, the remaining code after that point will be skipped until control either leaves the block or gets caught, so there is no "chain of failures".

[schwim2]

I think I'm botching up the implementation. I tried placing the query execution in the try brackets and it's continuing page generation even though the the query is malformed.

try{ 

$r_topics = mysqli_query($link, $q_topics);

}catch (mysqli_sql_exception $e){

echo 'Sorry, the site is not working at this time.';
$message = "db error: {$e->getmessage()}, File: {$e->getfile()}, Line: {$e->getline()},";
trigger_error($message, E_USER_ERROR);

} 

while ($row_topics = mysqli_fetch_array($r_topics, MYSQL_ASSOC)) {

I'm sure it's my attempt to move the existing query code with the try/catch stuff that's new to me. Could someone let me know what I need to change to make it work?

Thanks for your time!

[pbismad]

I should just run it at the end of the file?

The error handling code goes around your database dependent code. And if it isn't clear, you only have the posted code once. All your database dependent code goes inside the try {} block.

It would also help if you separated your database dependent code (that knows how to execute and fetch data from the queries), from the presentation code (that knows how to produce the output from the data.) The way to do this is to fetch the data from any query into an appropriately named php variable, then just use the php variable as input to the presentation code.

As to your current symptom, did you add the two lines of code setting the mysqli driver error mode to exceptions? These can be added at any point in the code, but putting them before the connection code will also cause the connection to throw an exception, letting you handled all the mysqli errors in one place with the just one instance of code.