how to manage errors server side (php) when Ajax is involved? - php

Question

So, I have an ajax call that prevents default post submission, server side I do some validation and checking, if the data is correct I do some database operations (inserting item for user etc) but if the data is not correct I don't have to make anything but throw out an error (i.e. item already present). My case in the controller was something like this:
} else {
print('Item already present');
}
but now I have the ajax call that manages the error like this:
error: function( xhr, status, errorThrown ) {
alert( "Sorry, there was a problem!" );
console.log( "Error: " + errorThrown );
console.log( "Status: " + status );
console.dir( xhr );
},
So obviously the php doesn't print anything.
How should I modify my php to act well with the ajax call?

Answer 1

When you make an ajax call, you should be expecting a particular type of data back. A typical (example) scenario is to get back data in JSON. If you are using jQuery, then I typically to look for errors in a two places because I think of ajax errors coming in two types:
network error or anything that results in a website error (404 - page not found, 500 - potential coding error, etc). This is caught in the ajax 'error' handler function as you have it above. I believe you could intentionally trigger an error in your PHP code to get this case.
logical error. This is an error that you might be expecting to handle - such as a bad username/password during a login call via ajax. In this case, you don't really want to throw a PHP error. Instead you want to return an error, but perhaps also include some meta data bout the error such as 'username does not exist' or whatever.
So, on your php server, you would have a view that needs to set the header to be a JSON response, and then output the JSON error, e.g.:
<?php
// output a json version of any list of objects that has the
// "toArray()" method defined.
// ...for ajax calls.
header( 'Content-type: application/json' );
$isError = 'false';
if (checkToSeeIfErrorOccurred())
{
$isError = 'true',
$errorMessage = getErrorMessages();
}
?>
<!-- define json result -->
{
error: "<?php echo $isError; ?>",
errorMessage: "<?php echo $errorMessage; ?>"
}
So, on your client side, in (for instance) your jquery ajax call, you would define a successHandler that needs to check for this error, and specify the dataType of the return value. Note that even though it is a successHandler, the 'success' part just means you had no network or programmatic/PHP error thrown. So, you still need to check for the logical error you might return in your JSON:
// your error handler
function myErrorHandler( xhr, status, errorThrown )
{
alert( "Sorry, there was a problem!" );
console.log( "Error: " + errorThrown );
console.log( "Status: " + status );
console.dir( xhr );
};
function mySuccessHandler( response )
{
// response is returned as an object
if (response.error === 'true')
{
// maybe call same error handler?
myErrorHandler( 'whoCares', 'logicalFailure', response.errorMessage );
}
else
{
// handle success
}
};
$.ajax(
url,
dataType: 'json',
error: myErrorHandler,
success: mySuccessHandler,
...
);
I don't know if this is typical for other folks and it is only an example but it has worked well for me...

Answer 2

One way you could think about this is use ajax to do your request and then return xml with a result from php echo statement. If the result is successful then your code does what it needs to do else as part of the php server return you have an xml error tag with why it went wrong and then process this in your ajax.
Another way you could return a result is with json.