Clearing out options when submitting an empty multiSelect form

[Aaron Valade]

Hello all-
I'm having an issue when trying to update a many-to-one collection
attached to a JPA object in Lift. I'm currently using a
SHtml.multiSelect for choosing which objects should be assigned to the
many-to-one collection. My bind statement looks like this:

bind("location", xhtml,
"id" -> SHtml.hidden(() => locationVar(current)),
"name" -> SHtml.text(location.name, location.name = _),
"beacons" -> SHtml.multiSelect(choices, default, {bsIds : List
[String] => {
location.beacons.clear
bsIds.map( id => location.beacons.add(Model.getReference(classOf
[Beacon], id.toLong) ) )
} } ),
"save" -> SHtml.submit(?("Save"), doAdd) )

This works great when I'm adding or removing beacons to my location as
long as I don't unselect all options. When I unselect all options, my
closure for the multiSelect doesn't get called so the beacons Set
doesn't get cleared out.

How can I capture when I unselect everything in my multiSelect?

Thanks in advance!
- Aaron

[Derek Chen-Becker]

What's happening here is that the form doesn't submit a field for "beacons" at all if nothing is selected, so the callback doesn't get called. What I typically do in scenarios like this is add a hidden field whose callback clears the collection. In your case, you could move the "location.beacons.clear" inside the hidden callback for "id" and have it all taken care of.

Derek

[Aaron Valade]

On Sep 16, 2009, at 1:07 PM, Derek Chen-Becker wrote:

> What's happening here is that the form doesn't submit a field for
> "beacons" at all if nothing is selected, so the callback doesn't get
> called. What I typically do in scenarios like this is add a hidden
> field whose callback clears the collection. In your case, you could
> move the "location.beacons.clear" inside the hidden callback for
> "id" and have it all taken care of.

Ah, I didn't think about adding that clear statement there. Thanks
Derek!

- A