JPA Native Query to map One to Many - jpa

Question

I have a complex Oracle query which for simplicity's sake looks like this;
SQL> SELECT d.id AS dept_id,
2 d.name AS dept_name,
3 e.id AS emp_id,
4 e.name AS emp_name,
5 e.dept_id AS emp_dept_id
6 FROM drs2_dept d, drs2_emp e
7 WHERE d.id = e.dept_id (+)
8 /
DEPT_ID DEPT_NAME EMP_ID EMP_NAME EMP_DEPT_ID
---------- ------------------- ---------- -------------- -----------
1 SALES 101 JOHN 1
1 SALES 102 JANE 1
2 ADMIN
My Department class is;
#SqlResultSetMapping(
name = "Department.employeeMapping",
classes = {
#ConstructorResult(
targetClass = Department.class,
columns = {
#ColumnResult(name = "DEPT_ID", type = Integer.class),
#ColumnResult(name = "DEPT_NAME")
}
),
#ConstructorResult(
targetClass = Employee.class,
columns = {
#ColumnResult(name = "EMP_ID", type = Integer.class),
#ColumnResult(name = "EMP_NAME"),
#ColumnResult(name = "EMP_DEPT_ID", type = Integer.class)
}
)
}
)
#NamedNativeQuery(
name = "Department.findAllEmployees",
query = "SELECT d.id AS dept_id, " +
" d.name AS dept_name, " +
" e.id AS emp_id, " +
" e.name AS emp_name " +
" e.dept_id AS emp_dept_id, " +
"FROM drs2_dept d, drs2_emp e " +
"WHERE d.id = e.dept_id (+)",
resultSetMapping = "Department.employeeMapping"
)
#Entity
public class Department {
#Id // JPA will not start without it.
Integer id;
String name;
#OneToMany // JPA will not start without it.
List<Employee> employees = new ArrayList<>();
public Department(Integer id, String name) {
this.id = id;
this.name = name;
}
public Department() {}
// getters and setters
}
My Employee class is;
#Entity
public class Employee {
#Id Integer id;
Integer departmentId;
String name;
public Employee(Integer id, String name, Integer departmentId) {
this.id = id;
this.name = name;
this.departmentId = departmentId;
}
public Employee() {}
// getters and setters
}
Because I am using #ConstructorResult I am able to get the data, but it still in a flat structure, that is to say a List<Object[]> with three entries, each containing [Department, Employee]. So I have to do the following to move the Employee records within their respective Department;
#Component
public class DepartmentDAO {
#PersistenceContext EntityManager entityManager;
public Collection<Department> getAllDepartments() {
Query query = entityManager.createNamedQuery("Department.findAllEmployees");
Map<Integer, Department> map = new HashMap<>();
List<Object[]> list = query.getResultList();
for (Object[] tuple: list) {
Department d = (Department) tuple[0];
if (! map.containsKey(d.getId())) {
map.put(d.getId(), d);
}
d = map.get(d.getId());
Employee e = (Employee) tuple[1];
if (e.getId() != null) {
d.getEmployees().add(e);
}
}
return map.values();
}
}
Whenever I add any additional properties to the #OneToMany I seem to get spurious SQL generated in the Hibernate logs which is incorrect (i.e. non-existent column or table names), but as I stated at the start of this question, I want the native SQL only - I don't want Hibernate to figure out what I am trying to do.
Is there any way to get JPA/Hibernate to put the Employee objects into the Department's list for me?
(
As a sub-note, I have seen this question asked here, but either never answered or answered back in 2011, by which time JPA and Hibernate may have progressed.
I should also add that elsewhere in my project I already have Department and Employee fully mapped for CrudRepository use with #Table and #Column, however their #OneToMany definitions do not depict what I am doing in the above query, hence their absence in my example code.
)

Answer 1

This query does not have any clause that forces it to be implemented with a native.
In fact it is considered a bad practice.
Try this:
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Departament> cq = cb.createQuery(Departament.class);
Root<Departament> rootDepartament = cq.from(Departament.class);
Join<Departament,Employee> joinEmployee = rootDepartament.join(Departament_.employees,JoinType.Left);
cq.select(rootDepartament);
List<Departament> result = entityManager.createQuery(cq).getResultList();