在@ManyToOne侧合并托管实体 [英] Merging a managed entity on the @ManyToOne side

问题描述

从部门到员工。

下给出一对多关系。

部门（家长）：

  @OneToMany（mappedBy =department，fetch = FetchType。 LAZY，cascade = CascadeType.ALL）
私人列表< Employee> employeeList = new ArrayList< Employee>（0）; 
  

员工（子女）：

  @JoinColumn（name =department_id，referencedColumnName =department_id）
 @ManyToOne（fetch = FetchType.LAZY，cascade = {CascadeType.PERSIST，CascadeType.MERGE，CascadeType.REFRESH ，CascadeType.DETACH}）
私人部门部门; 
  

合并如下的托管实体（子项）（在EJB中使用CMT），

  Employee employee = entityManager.find（Employee.class，1L）; 
 employee.setDepartment（department）; //部门由客户提供。 
 employee.setEmployeeName（xyz）; 
 entityManager.merge（employee）; 
  

不会更新数据库表中相应的员工行。只有当 CascadeType.MERGE 从子$ @ManyToOne 关系中< Employee 。

为什么表中的行没有被更新？ CascadeType.MERGE 关于这个例子的唯一目的是什么？

我目前使用EclipseLink 2.6.0 JPA 2.1。

解决方案

级联应始终从父级传播到子级而不是相反。

在你的情况下，你需要从子端删除Cascade：

  @JoinColumn（name =department_id ，referencedColumnName =department_id）
 @ManyToOne（fetch = FetchType.LAZY）
私人部门部门; 
  

并确保您设置关联的双方：

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

Given below a one-to-many relationship from Department to Employee.

Department (parent) :

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

Employee (child) :

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

Merging a managed entity (child) like the following (using CMT in EJB),

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

does not update the corresponding employee row in the database table. It happens only when CascadeType.MERGE is removed from the child @ManyToOne relationship in Employee.

Why doesn't the row in the table get updated? What is the sole purpose of CascadeType.MERGE regarding this example?

I am currently using EclipseLink 2.6.0 having JPA 2.1.

解决方案

Cascading should always propagate from a Parent to a Child and not the other way around.

In your case, you need to remove the Cascade from the child-side:

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

and make sure you set both sides of the association:

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

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