You can download the sample workspace from here.
[Runs with Oracle JDeveloper 18.104.22.168.0 (11g R2) + HR Schema]
A glance at the implementation
1. Run test.jspx
2. Data source for LOV defined on ManagerId changes based on the values keyed in for DepartmentId field. If you leave Department empty, data is queried from EMPLOYEES table. If DepartmentId present for the row data for LOV is queried from DEPARTMENTS table for DepartmentId. The query switching is done programmatically from the over ridden prepareRowSetForQuery(...) method. Note that ViewObject definition doesn't change in the implementation, query alone changes.
Please see ManagerViewObjImpl::prepareRowSetForQuery(ViewRowSetImpl vrs) to learn more about the query switching details.