Loading ALL data via 'Data on Demand' when NULL value doc property
I'm trying to build a simple querying tool for my webplayer users. The front end is connected to a query I've written in Transact-SQL.
The user should be able to select a number of parameters, such as Department, Category, Branch etc. However, none of these selections is mandatory and if the Document Property is not selected (ie. NULL) I'd like Spotfire to interpret that as ALL data to be returned for that column. For example, user selects 'Menswear' from Department dropdown and Menswear data returned. User chooses NOT to select any department and ALL departments returned (Mens+Womens+Childrens).
Perhaps I can set Data on Demand input from an Expression rather than Property?
I think I've seen this done before but I can't see anything on this site or via search engines.
Any ideas, please?
Thanks in advance.