我的 Spring JPA 应用程序中有三个独立的实体 - 用户、部门、角色
我的数据库中有一个连接表来关联这些实体中的每一个:USER_DEPARTMENT_ROLE
我的问题是,如何在我的实体类中定义这种关系?我是否必须在每个单独的实体中定义一个 @ManyToMany
关系?我知道如何定义两个表之间的这种关系,但对于两个以上的表,我不确定从哪里开始。
感谢任何帮助!
最佳答案
如果您在连接表中映射了两个以上的关系,那么我建议创建一个单独的实体,用于映射该特定表。
问题是您是否可以有一个不同的 id 列作为人工主键,或者您必须坚持使用三个外键构建的复合主键。
如果您可以添加人工 ID(这是设计数据库的现代方式),那么您的映射应该如下所示:
选项 1
class User {
@OneToMany(mappedBy = "user", cascade = {CascadeType.PERSIST, CascadeType.MERGE})
private Set<UserDepartmentRoleLink> userDepartmentRoleLinks;
}
class Department{
@OneToMany(mappedBy = "department", cascade = {CascadeType.PERSIST, CascadeType.MERGE})
private Set<UserDepartmentRoleLink> userDepartmentRoleLinks;
}
class Role{
@OneToMany(mappedBy = "role", cascade = {CascadeType.PERSIST, CascadeType.MERGE})
private Set<UserDepartmentRoleLink> userDepartmentRoleLinks;
}
class UserDepartmentRoleLink {
@Id
@GeneratedValue
private Long id;
@ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
@JoinColumn(name = "user_id")
private User user;
@ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
@JoinColumn(name = "department_id")
private Department department;
@ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
@JoinColumn(name = "role_id")
private Role role;
}
关于为多对多关系设置级联类型是棘手的,对于涉及三个表的多对多甚至更棘手,因为每个实体都可以根据情况扮演 parent 或 child 的角色..我建议只坚持cascade = {CascadeType.PERSIST, CascadeType.MERGE}
并手动处理其他操作。
如果您必须保留复合主键,那么您应该添加额外的 Id 类并将链接实体更改为以下内容:
选项 2
class User {
@OneToMany(mappedBy = "linkPk.user", cascade = {CascadeType.PERSIST, CascadeType.MERGE})
private Set<UserDepartmentRoleLink> userDepartmentRoleLinks;
}
class Department{
@OneToMany(mappedBy = "linkPk.department", cascade = {CascadeType.PERSIST, CascadeType.MERGE})
private Set<UserDepartmentRoleLink> userDepartmentRoleLinks;
}
class Role{
@OneToMany(mappedBy = "linkPk.role", cascade = {CascadeType.PERSIST, CascadeType.MERGE})
private Set<UserDepartmentRoleLink> userDepartmentRoleLinks;
}
链接表
class UserDepartmentRoleLink {
@EmbeddedId
private UserDepartmentRoleLinkId linkPk
= new UserDepartmentRoleLinkId();
@Transient
public User getUser() {
return getLinkPk().getUser();
}
@Transient
public User getDepartment() {
return getLinkPk().getDepartment();
}
@Transient
public User getRole() {
return getLinkPk().getRole();
}
}
@Embeddable
public class UserDepartmentRoleLinkId implements java.io.Serializable {
@ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
@JoinColumn(name = "user_id")
private User user;
@ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
@JoinColumn(name = "department_id")
private Department department;
@ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
@JoinColumn(name = "role_id")
private Role role;
最重要的是,您可以像这篇文章中概述的那样在这里使用多对多 -> example .但在我看来,如果您像上面那样映射链接表,您会省去很多麻烦。最后是你的电话..
关于java - @ManyToMany 三个表之间的关系,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/42488559/