Hibernate CriteriaQuery where - ManyToOne field - spring

Question

that's fragment of my Employee entity/class:
#Entity
#Table
public class Employee {
...
#ManyToOne(.....)
#JoinColumn(name="department_id")
private Department department;
}
Now, I want to fetch all Employees from specific Department (employees with specific department_id):
CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Employee> criteriaQuery = builder.createQuery(Employee.class);
Root<Employee> employeeRoot = criteriaQuery.from(Employee.class);
criteriaQuery.select(employeeRoot);
criteriaQuery.where(builder.equal(employeeRoot.get(????????????), id));
There's my problem. How do I access Department.id? I know i have to get({specific field}) but i dunno how. Should I somehow join those tables first? Looking forward for your answers!

Answer 1

You need create a join with your relationed table.
Ex:
CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Employee> criteriaQuery = builder.createQuery(Employee.class);
Root<Employee> employeeRoot = criteriaQuery.from(Employee.class);
Join<Employee, Departament> join = from.join("department", JoinType.INNER);
criteriaQuery.where(builder.equal(join.get("specific_fied"), your_specific_fied));
TypedQuery<Employee> typedQuery = session.createQuery(criteriaQuery);
List<Employee> employees = typedQuery.getResultList();
for (Employee e : employees) {
System.out.println(e.getName());
}
session.getTransaction().commit();
session.close();
entityManagerFactory.close();
If you want anything same as this query:
SELECT c, p.name FROM Country c LEFT OUTER JOIN c.capital p
you can build this:
CriteriaQuery<Country> q = cb.createQuery(Country.class);
Root<Country> c = q.from(Country.class);
Join<Country> p = c.join("capital", JoinType.LEFT);
q.multiselect(c, p.get("name"));
If you what build anything same as this query:
SELECT c FROM Country c JOIN FETCH c.capital
you can build this:
CriteriaQuery<Country> q = cb.createQuery(Country.class);
Root<Country> c = q.from(Country.class);
Fetch<Country,Capital> p = c.fetch("capital");
q.select(c);
For more exemples see FROM clause (JPQL / Criteria API)