Java JPQL和外部连接

我对这个简单的左连接有这个问题

我有两张桌子： 员工和部门

员工与部门有多对一关联：

public class Employee {
    @Id
    @Column(name = "ID")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_EMPLOYEE")
    private Long id;

    @Column(name = "NAME")
    private String name;

    @Column(name = "SURNAME")
    private String surname;

    @ManyToOne()    
    private Department department;

@Entity
@Table(name = "DEPARTMENT")
@SequenceGenerator(name = "SEQ_DEPARTMENT", sequenceName = "SEQ_DEPARTMENT", allocationSize = 1)
public class Department {

    @Id
    @Column(name = "ID")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_DEPARTMENT")
    private Long id;

    @Column(name = "NAME")
    private String name;

及部门：

public class Employee {
    @Id
    @Column(name = "ID")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_EMPLOYEE")
    private Long id;

    @Column(name = "NAME")
    private String name;

    @Column(name = "SURNAME")
    private String surname;

    @ManyToOne()    
    private Department department;

@Entity
@Table(name = "DEPARTMENT")
@SequenceGenerator(name = "SEQ_DEPARTMENT", sequenceName = "SEQ_DEPARTMENT", allocationSize = 1)
public class Department {

    @Id
    @Column(name = "ID")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_DEPARTMENT")
    private Long id;

    @Column(name = "NAME")
    private String name;

关于数据库

SELECT * FROM EMPLOYEE;
ID      NAME    SURNAME     DEPARTMENT_ID  
1   Massimo Ugues   1
2   Mazi    Ugues   2

SELECT * FROM DEPARTMENT;
ID      ADDRESS     NAME  
1   Via Gaber   Le betulle

因此，有一名员工不属于任何部门

现在我需要加载id为2的员工，即在Db中不存在的部门id为2的员工

这就是JPQL查询：

select e, department from Employee e left outer join e.department department where e.name = :name and department.id = :id

这是生成的相对sql：

SELECT t0.ID, t0.NAME, t0.SURNAME, t0.DEPARTMENT_ID, t1.ID, t1.ADDRESS, t1.NAME FROM {oj EMPLOYEE t0 LEFT OUTER JOIN DEPARTMENT t1 ON (t1.ID = t0.DEPARTMENT_ID)} WHERE ((t0.NAME = ?) AND (t1.ID = ?))
    bind => [Mazi, 2]

问题不在联接中，而是在

t1.ID=？

中。它应该是t0.ID=？其中t0是employee表

你知道怎么做吗

亲切的问候。

---

Massimo

问题不在于休眠。问题是你的数据库。如果员工不属于任何部门，则在

department\u id

列中应该有

NULL

，而不是一些不存在的部门id。您应该对

employee.department\u id

设置外键约束，以确保不会发生这种不一致。这是酸中的C

因此，我的建议是：修复数据：

update employee set department_id = null where department_id not in (select id from department)

---

另外，请注意，执行左连接并强制部门具有特定ID与执行内部连接相同

是的，那将是最好的解决办法。但由于我有一个lagacy数据库，所以我必须处理这样的问题，我需要某种方法来按姓名和departmentId加载一个可能不一致的departmentId值的员工。在DB上，我没有引用完整性。一种解决方案是将departmentId作为字符串属性处理。是否有另一种解决方案来维持员工和部门之间的关联，并实现目标？亲切的问候。Massimo您可以使用NotFound注释。看见但是，您的查询不会加载员工，因为它要求有特定部门的员工。您可以使用select e from Employee，其中e.name=：name和e.department.id=：id。但我认为您将在一段时间后被这种缺乏完整性的情况所困扰。我正在使用eclipse链接作为JPA提供者而不是hibernate编写纯JPA。