Spring Data: Fetching values from Entity with #ElementCollection - jpa

Question

My Entity class is:
#Entity
#Data
#Table(uniqueConstraints = { #UniqueConstraint(columnNames = {"username" }, name = "uq_username") } })
public class User{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#NotNull
private String firstName;
private String lastName;
#ElementCollection(targetClass = Role.class,fetch = FetchType.LAZY)
#JoinTable(name = "User_Roles", joinColumns={#JoinColumn(name = "user_id")})
#Enumerated(EnumType.STRING)
private List<Role> roles;
}
Role class is an enumeration:
public enum Role {
ADMIN,
OFFICE_USER,
SUPERVISOR,
MANAGER,
DATA_ENTRY
}
Property spring.jpa.hibernate.ddl-auto=create and the tables user and user_roles (fields: user_id, roles) are created and data inserted successfully. However, querying for data for users with a role is not working. My repository is:
#Component
public interface UserRepository extends CrudRepository<User, Integer>, JpaRepository<User, Integer> {
#Query(value = "select usr from User usr where usr.firstName LIKE :username% OR usr.lastName LIKE :username%"
+ " AND usr.roles=:roles")
public List<User> fetchUsersByNameAndRole(String username, Collection<String> roles);
}
On passing the following request I am getting error
http://localhost:8080/api/users/search/fetchUsernamesByNameAndRole?username=Thom&roles=SUPERVISOR
[org.springframework.data.rest.webmvc.ResourceNotFoundException: EntityRepresentationModel not found!]
If I change Repository method (changing username parameter to String from Collection) to
#Query(value = "select usr from User usr where usr.firstName LIKE :username% OR usr.lastName LIKE :username%"
+ " AND usr.roles=:roles")
public List<User> fetchUsersByNameAndRole(String username, String roles);
The error becomes:
[org.springframework.dao.InvalidDataAccessApiUsageException: Parameter value [SUPERVISOR] did not match expected type [java.util.Collection (n/a)]; nested exception is java.lang.IllegalArgumentException: Parameter value [SUPERVISOR] did not match expected type [java.util.Collection (n/a)]]
Question 1: How can I fetch all users with a name and a particular role (or set of roles) in this scenario?
The code is working if I remove the roles clause, like
#Query(value = "select usr from User usr where usr.firstName LIKE :username% OR usr.lastName LIKE :username%")
public List<User> fetchUsersByName(String username);
I need the user names only. So I changed code to:
#Query(value = "select usr.firstName from User usr where usr.firstName LIKE :username% OR usr.lastName LIKE :username%")
public List<String> fetchUsersByName(String username);
But gets the error:
org.springframework.data.mapping.MappingException: Couldn't find PersistentEntity for type class java.lang.String
Changing to native query also gives same error:
#Query(value ="select first_name from user where first_name like ?1%", nativeQuery = true)
Question 2: Why mapping to List is not working in Spring data? I remember it was working with normal Spring JPA