Multiple M2M in PowerPivot: To solve multiple M2M >> use nested Calculate multiple times, each time for 1-step M2M.
Promotion – Product – Order:
Order is M2M with Product. This necessitates another table to materialize this M2M relationship. Let’s call it: OrderProductM2M.
Product is M2M with Promotion. Likewise to materialize this relationship, let’s call the new table PromotionProductM2M.
To know the count of orders that a promotion triggered, using DAX:
CALCULATE( CALCULATE( COUNTROWS( Order),Product, OrderProductM2M ),Promotion,PromotionProductM2M )