Spring Data Mongodb Extracting Parts of a Sub-Documents

Question

I am using spring-data-mongodb 1.9.1.

My question is pretty similar to this one.

I have

@Document
 public class Employee{

 private int userId;
 private List<Address> addresses;
 }

And

@Document
public class Address{

 private int addressId;
 private String street;
 private String city:
 }
// Getters and setters

I have written a query and can get the value I need returned as an Employee object.

 @Query(value="{ '$and' : [ {'addresses.city' : ?0 }]} ", fields="{ 'addresses.street' : 1}")
    List<Employee> findStreetByEmployeeId(String fieldName);

My question is how can I get

List<String> findStreetByEmployeeId(String fieldName);

In other words, I want to just extract the part of the result in which I am interested. If I have to loop through all Employee objects and extract the populated street value, it can become a very expensive operation.

Any thoughts on how to achieve this would be much appreciated. Thanks.