Generate

The Generate function applies a second set to each member of a first set, performing a union of the results. Duplicates are dropped by default but can be retained with “,ALL”.
Although Generate doesn’t really do anything unique in itself it is a very useful way of shortening what would otherwise be long, laborious and error-prone queries.

In the following example the top performing child product is returned for each member of Level 1 of the hierarchy:
{Filter(
GENERATE(
{TM1FILTERBYLEVEL( {TM1SUBSETALL( [Product] )}, 1)},
TopCount(Descendants([Product].CurrentMember, 1),1,Test.([Posting Measures].[Amount])))
,Test.([Posting Measures].[Amount]) > 0
)}