java如何在数据库中有空值的JPA实体中迭代联接列

Question

我在迭代部门时遇到问题。当数据库中的部门id值为空时。当我试图得到部门。部门id

for (int i = 0; i < listEmp.size(); i++) {
  employeeMap.put("empDeptId" + i, StringUtil.isDataNull(listEmp.get(i).Departments.DEPARTMENT_ID));[enter image description here][1]
}
return employeeMap;

在我的员工实体中，我有一个部门的联接列

@Entity
@Table(name="EMPLOYEES")
@SequenceGenerator(name = "EMPLOYEES_SEQ", sequenceName = "EMPLOYEES_SEQ")
public class Employees {

  @ManyToOne(optional = true)
  @JoinColumn(name= "DEPARTMENT_ID",nullable = true)
  public Departments Departments;

} 

部门和实体

@Entity
@Table(name="DEPARTMENTS")
public class Departments {

  public Integer DEPARTMENT_ID;

  public String DEPARTMENT_NAME;

}

更新： 找到了工作

if (listEmp.get(i).Departments == null)
  employeeMap.put("empDeptId" + i, "");
else
  employeeMap.put("empDeptId" + i, StringUtil.getStrFormat(listEmp.get(i).Departments.DEPARTMENT_ID));

但有没有办法解决这个问题，仅仅利用员工。上课