Rails - Sep 2009 - collection_select on controller update actions

When doing a controller update operation, missing parameters are
treated as unchanged.  This is a great convention but I''m not sure how
to handle this when using a collection_select.

If a user deselects all items in a the HTML select, nothing is sent on
the update action.

For example, if 2 items are selected I get
params[:selected_location_ids] == ["22", "242"]

if no items are selected the params[:selected_location_ids] is not
sent.

Is there a way to make the HTML form send an empty option when nothing
is selected so I can know if the user deselected everything vs an
alternate form not sending this information?

Try passing a hidden_field_tag with the location_ids set to blank
underneath the collection_select.

ex:

<%= hidden_field_tag ''[selected_location_ids][]'' %>



On Sep 16, 1:50 pm, Tony
<tony.primer...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> When doing a controller update operation, missing parameters are
> treated as unchanged.  This is a great convention but I''m not sure
how
> to handle this when using a collection_select.
>
> If a user deselects all items in a the HTML select, nothing is sent on
> the update action.
>
> For example, if 2 items are selected I get
> params[:selected_location_ids] == ["22", "242"]
>
> if no items are selected the params[:selected_location_ids] is not
> sent.
>
> Is there a way to make the HTML form send an empty option when nothing
> is selected so I can know if the user deselected everything vs an
> alternate form not sending this information?