[whatwg] Any way to submit only those parts of a form that havechanged?

Ian Hickson ian at hixie.ch
Mon Dec 13 13:36:46 PST 2004

On Sun, 12 Dec 2004, Ben Meadowcroft wrote:
> > >
> > > I don't feel like doing a detailed readthrough of the spec again 
> > > (though I did glance at parts that looked relevant), but is there 
> > > anything in WF2 that allows only parts of a form that have changed 
> > > from their default value to be submitted?
> > 
> > There isn't; what would the use case be?
> Seriously though I recently had to frig this by adding hidden form 
> elements using Javascript to the form on an onchange handler indicating 
> when a field had been changed so you don't have to do lookups on the 
> backend data first to decide if there has been a change or not.

Be very careful with this -- you should always assume that the 
client-provided data is hostile, and not trusted.

> You can then dynamically construct an update statement (in SQL say) that 
> only updates those fields that have changed (Which might be important if 
> updating certain fields could lead to lots of potentially expensive 
> trigger knock ons in the database).

It's quite possible that the field changed while the page was being shown 
to the user, though, for example if the user loaded the page twice, 
modified the pages differently, and then submitted both, or if two users 
did the same thing (unknowingly). Since different databases would have 
different ways of handling this, I don't know that we would want the UA to 
be doing anything about it. It seems like it would be best to let the 
server handle it as appropriate.

(Note that there is also the problem of how to handle checkboxes that I 
mentioned earlier. Any proposal for how to handle this would have to 
address that issue first.)

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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