合并@ManyToOne方面的托管实体

Question

下面给出从Department到的一对多关系Employee。

部门（家长）：

@OneToMany(mappedBy = "department", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private List<Employee> employeeList = new ArrayList<Employee>(0);

员工（孩子）：

@JoinColumn(name = "department_id", referencedColumnName = "department_id")
@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH, CascadeType.DETACH})
private Department department;

合并如下所示的托管实体（子实体）（在EJB中使用CMT），

Employee employee = entityManager.find(Employee.class, 1L);
employee.setDepartment(department); // department is supplied by a client.
employee.setEmployeeName("xyz");
entityManager.merge(employee);

不会更新数据库表中的相应员工行。仅当CascadeType.MERGE从中的子@ManyToOne关系中删除时，才会发生这种情况Employee。

为什么表中的行没有更新？CascadeType.MERGE关于此示例的唯一目的是什么？

我当前正在使用具有JPA 2.1的EclipseLink 2.6.0。

Answer 1

级联应该始终从父级传播到子级，而不是相反。

在您的情况下，您需要从子级移除级联：

@JoinColumn(name = "department_id", referencedColumnName = "department_id")
@ManyToOne(fetch = FetchType.LAZY)
private Department department;

并确保设置了关联的两面：

Employee employee = entityManager.find(Employee.class, 1L);
employee.setDepartment(department);
employee.setEmployeeName("xyz");
department.getEmployeeList().add(employee);
entityManager.merge(department);