[Seaside] Ajax and error management

[Philippe Marschall]

2011/5/14 Johan Brichau <johan at inceptive.be>:
> Thierry,
>
> Exceptions in Seaside are handled by an instance of (a subclass of) WAExceptionHandler. Setting the exception handler is part of the application configuration.
> For development, Seaside provides you with exception handlers (e.g. WAWalkbackErrorHandler) that return an exception page and that can open a debugger on the server-side (or they put a continuation on the objectlog in GLASS).
> However, the problem with AJAX calls is that the browser will not render that response as a page refresh. Gracefully dealing with those exceptions requires a bit of javascripting. In addition, if you want to handle exceptions differently on the server-side, you need to implement your own subclass of WAExceptionHandler (or any of its subclasses).
>
> For handling ajax errors differently on the client side (for example, refreshing the page anyway): provide a javascript function as the 'onError' parameter for the ajax call. You can do this for each ajax call separately, or you can define a global handler.
> Some examples:
> - http://stackoverflow.com/questions/377644/jquery-ajax-error-handling-show-custom-exception-messages
> - http://api.jquery.com/ajaxError/
>
> To change the server-side behavior. I think you can find your way by looking at the implementation of the existing handlers.
> To give you yet another example, here is the principal code of an error handler we are using in production code. In combination with a global ajax error handler, it makes sure that a decent error message is put on the screen (in a kind of dialog window) whenever an error occurred server-side in an ajax callback.
>
> handleDefault: anException
>        [self logErrorToDisk: anException]
>                ensure: [self requestContext respond: [ :response |
>                                                                response
>                                                                        internalError;
>                                                                        contentType: WAMimeType textHtml;
>                                                                        nextPutAll: (self rendererClass builder
>                                                                                fullDocument: true;
>                                                                                rootBlock: [ :root | root title: anException description ];
>                                                                                render: [:html | html render:(NPProductionErrorDialog exception: anException)])]]
>
>
> Hope this gets you on your way!

Nice summary. Note that there is WARequest >> #isXmlHttpRequest that
allows you to write special error handling code for AJAX. If you want
to handle the error on the client side you need to set the HTTP status
code (WARespnse >> #status:) to some server error (5xx). Note that
there are at least two ways to display an error page with JavaScript
error handling code. Either by redirecting to it with window.location
or by just simply changing the DOM.

Cheers
Philippe