Dimensional - Filtering two dimensions using one prompt

[LDJB81]

Hi all,

I have created a tree prompt based on a Product Dimension and I would like to use the prompt selection to also filter a Product Market Dimension where the products in both dimensions come from the same relational source (same captions and business keys). The client doesn't want 2 prompt controls but in the calculation below I need to have both dimensions filtered on the same product for it work correctly. It's worth mentioning that the cube technology is SSAS 2008 and there is a many to many join between these dimensions in the cube via a bridge table.

aggregate (Market Share Measure
within set
Product Prompt,
Time Prompt,
"Product Market Expression")

For the Product Market expression I was thinking of using a filter function and then extracting the business keys using roleValue but it didn't work. I also looked at a substitute macro but there was another level in the product market dimension meaning there was an extra number in the MUN.

Can anybody help?

Thanks
Lloyd