want to select attribute for dropdown

Hi all, I want to select attribute for a field which is in dropdown but it is not giving me the option to select . Also what i want in dropdown ..there is a heirarchical levels if the junior is the user then his manager will be his/her senior . but if the senior will be the user then his manager should be  a super senior. andthat is why user role is also there so that it will show which post the user is holding .  on the entity we have used self join so that one user can have multiple manager options      given below is the entity which I’m using : Please advice .
1 answers

In order to be able to select from a drop-down, the data type of your attribute should be an enumeration. See https://docs.mendix.com/refguide/drop-down for more details. So as Sufian wrote already, you should use a a reference selector.