Make a dependent input display NO options, when no options are selected from the parent input

[andey.wei]

I have two inputs. "Sites" & "Controllers". Controllers are the children of Sites. 

"Controllers" Custom Input Query

select id, name from controllers where $X{IN, site_id, site_id_1}[/code]

When site_id_1 has nothing selected

I expect: the return set to be empty
I get: all the controllers in the DB

Question: How do I make the query return no results when site_id_1 has no options selected?

What I've tried:

select id, name from controllers where (case when ($P{site_id_1} = null) then id = 0 else $X{IN, site_id, site_id_1} end)[/code]

However I don't know the data type of $P{site_id_1}, thus I don't know how to write an expression to test if the parameter is empty.

Thanks in Advance!

[hozawa]

Why don't you just check the input parameter? Do something like in the following thread but replace MyVerifiedParam default to something that'll return no result.

http://community.jaspersoft.com/questions/537583/validate-input-controls

[andey.wei]

I would like to check the parameter, but I'm not sure how. I tried "CASE WHEN ($P{site_id_1} = NULL)", but it always will fail that check.