Hibernate CriteriaQuery where - ManyToOne字段

Question

这是我的Employee实体/类的片段：

@Entity
@Table
public class Employee {
   ...
   @ManyToOne(.....)
   @JoinColumn(name="department_id")
   private Department department;
}

现在，我想从特定部门获取所有员工(具有特定department_id的员工)：

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));

这就是我的问题。如何访问Department.id？我知道我必须获取({特定字段})，但我不知道如何获取。我应该以某种方式首先加入这些表吗？期待您的回答！

Answer 1

您需要创建一个与关系表的连接。例如：

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();

如果您想要与此查询相同的任何内容：

SELECT c, p.name FROM Country c LEFT OUTER JOIN c.capital p

您可以构建以下内容：

  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"));

如果您构建了与此查询相同的内容：

SELECT c FROM Country c JOIN FETCH c.capital

您可以构建以下内容：

  CriteriaQuery<Country> q = cb.createQuery(Country.class);
  Root<Country> c = q.from(Country.class);
  Fetch<Country,Capital> p = c.fetch("capital");
  q.select(c);

有关更多示例，请参阅FROM clause (JPQL / Criteria API)