Submitting Multiple Forms At The Same Time (Edit Profile Page)
I've used django on most of my webapps, but the concept should be the same; I use ajax to send the data to the backend whenever the user hits submit (and the form returns false) so the user can keep editing it.  With ajax, you can send the data to different handlers on the backend.  Also, using jQuery, you can set flags to see if fields have been changed, to avoid sending the ajax message in the first place.  Ajax requests behave almost exactly like standard HTTP requests, but I believe the header indicates AJAX.
If you're looking at strictly backend, then you will need to do multiple "if" statements on the backend and check one field at a time to see if it has been changed. On the backend you should still be able to call other handlers (passing them the same request).
My question I suppose is rather simple. Basically, I have a profile. It has many variables being passed in. For instance, name, username, profile picture, and many others that are updated by their own respective pages. So one page would be used to update the profile picture, and that form would submit data from the form to the handler, and put() it to the database. What i'm trying to do here, is put all of the forms used to edit the profile on one single page at the same time.
Would I need one huge handler to deal with that page? When I hit 'save' at the bottom of the page, how do I avoid overwriting data that hasn't been modified? Currently, say I have 5 profile variables, they map to 5 handlers, and 5 separate pages that contain their own respective form.
Thanks.