This can be achieved as follows;
For example, for a lease contract, you need to select a specific building in the first selector and you want to have a list of apartments of that building in the second reference selector (drop down)
Therefore you need this domain model setup
This will be the page; data view with 2 reference selectors over associations;
The selectable objects in the Apartment selector can restricted by
1. datasource: XPath
2. Constrained by: select the path which limits the Apartments which have a association to the Building, which is also referenced by the Contract. Just tick in the box in front of the desired path.
Note that in my example there is only one option, in case of a more complex domain model it can be multiple DIFFERENT paths
HI Jawed Quamer,
You can add Constrained by option in refrence selector under Selectable objects, which will help you use case.