Using Entity Graph with DTO Projection using ResultTransformer returns null value - spring

Question

Hello I am new in jpa + criteria API + hibernate..
I have doubt related to use of ResultTransformer in jpa criteria API.
I am having two entity Department and Employee. one to many mapping between department and employee. i want to use entitygraph with DTO projection
1. Department
#Entity
#NamedEntityGraph(name = "departmentWithEmployee", attributeNodes = #NamedAttributeNode("setOfEmployee"))
#Table(name = "tblDepartment")
public class Department {
#Id
private String id;
private String name;
#OneToMany(mappedBy = "department")
private Set<Employee> setOfEmployee;
//....getter & setter
}
2. Employee
#Entity
#Table(name = "tblEmployee")
public class Employee {
#Id
private String id;
#ManyToOne
#JsonIgnore
private Department department;
private String firstName;
private String lastName;
//...getter & setter
}
DepartmentDTO.java
public class DepartmentDTO implements Serializable {
private String id;
private String name;
private Set<EmployeeDTO> setOfEmployee;
//... getter & setter..
}
I am executing query with entity graph and I want to get all departments from database and serialize with DepartmentDTO.java
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<DepartmentDTO> criteria = builder.createQuery(DepartmentDTO.class);
Root root = criteria.from(Department.class);
criteria.select(root);
EntityGraph graph = entityManager.getEntityGraph("departmentWithEmployee");
List<DepartmentDTO> list = entityManager.createQuery(criteria).setHint("javax.persistence.fetchgraph", graph)
.unwrap(org.hibernate.Query.class).setResultTransformer(Transformers.aliasToBean(DepartmentDTO.class)).list();
when i will get size of list it will give me correct result but it will give list of department with null value like
(In database i am having total 3 departments)
Output :
[
{
"id": null,
"name": null,
"setOfEmployee": null
},
{
"id": null,
"name": null,
"setOfEmployee": null
},
{
"id": null,
"name": null,
"setOfEmployee": null
}
]
I am getting all fields with null value.
So what is the issue here , is any mistake in use of ResultTransformer? Or is any better way to execute this query where I can get records using DTO ..?