So i assume you want 2 drop downs
where 1st dropdown is from database and 2nd dropdown is dependent on 1st one.
Lets asssume you have 3 entities
Entity 1 is DMA (In your case)
Entity 2 is dropdown 1
Entity 3 is dropdown 2
So keep DMA as Dataview and Inside that call a non persistent data view (create a non persistent entity and have 1-* association with Entity 2 ) Make that non persistent data view’s datasource as microflow , open that microflow and do as follows
Retrieve entity 2 → create object (Map the non persistent association)→ iterate over Entity 2 → inside loop change the created object and map it → make sure you return the object
Once these steps are done
You will have DMA Data view and inside that non persistent’s data view ,Now inside the non persistent’s data view call another data view of with entity 3 (make sure you have an 1-1 association between entity 2 and 3),Later call another reference selector inside that (make sure it is 1-1 association) double click on reference selector , go to selectable objects call a microflow and do as follows
Retrieve entity 2 → over association call 1-* association between entity 2 and 3
To check if its working save entity 2 data independently and entity 3 data in entity 2 in separate pages , so that it reflects in your DME page.