java - 如何用JPA管理多个实体？

Question

上下文

我正在尝试创建一个简单的 API 来学习 Spring Boot 和 JPA。信息存储到H2数据库中。

我有 2 个实体:mission 和 user 。

多个用户被分配到一个任务。用户可以被分配到不同的任务。

所以，我的类 Mission 有一个属性 private ArrayList<User> users; 。

目标

我的目标是创建一些请求:

• (GET 请求)IP/missions/123456/users:获取分配给任务 123456 的所有用户
• (PUT 请求)IP/missions/456789:为用户分配任务 456789

因此，将两个实体绑定(bind)在一起。

有问题

但我不知道如何存储/绑定(bind)与 mission 和 user 相关的信息。好的方法是使用 Assignements(id_user, id_mission) 方案创建一个“关联表”？

感谢您的帮助!

编辑 1:代码

实体任务

@Entity
public class Mission{

    @Id
    private String id;
    private String name;
    private Date start;
    private Date end;
    private ArrayList<User> users;
    private int status;

    public Mission() {
    }

    public Mission(String name, Date start, Date end) {
        this.name = name;
        this.start = start;
        this.end = end;
        this.status = 0;
    }

    // getters and setters
}

实体用户

@Entity
public class User {

    @Id
    private String id;
    private String name;

    public User() {
    }

    public User(String name) {
        this.name = name;
    }

    // getters and setters
}

SQL

我使用 SQL 脚本。目前，脚本如下所示:

INSERT INTO mission (id, name, start, end, status) VALUES ('de7d9052-4961-4b4f-938a-3cd12cbe1f82', 'mission 1', '2019-02-11', '2019-02-13', 0)
INSERT INTO mission (id, name, start, end, status) VALUES ('425e7701-02c6-4de3-9333-a2459eece1c8', 'mission 2', '2019-02-10', '2019-02-15', 0)

编辑 2:新代码(使用 @ManyToMany)

实体

@Entity
public class Mission {

    @Id
    private String missionid;
    private String namemission;
    private Date start;
    private Date end;
    @ManyToMany
    @JoinTable(name = "mission_user",
        joinColumns = @JoinColumn(name = "missionid"),
        inverseJoinColumns = @JoinColumn(name = "userid")
    )
    private Set<User> users = new HashSet<>();
    private int status;

    public Mission() {}

    public Mission(String name, Date start, Date end) {
        this.namemission = name;
        this.start = start;
        this.end = end;
        this.status = 0;
    }
}

@Entity
public class User {

    @Id
    private String iduser;
    private String nomuser;
    @ManyToMany(mappedBy = "users")
    private Set<Mission> missions = new HashSet<>();

    public User() {}

    public User(String nom) {
        this.nomuser = nom;
    }

}

存储库

@RepositoryRestResource(collectionResourceRel = "mission")
public interface MissionResource extends JpaRepository<Mission, String> {
    ...
}

@RepositoryRestResource(collectionResourceRel = "user")
public interface UserResource extends JpaRepository<User, String> {
    ...
}

休息 Controller

@RestController
@RequestMapping(value = "/missions", produces = MediaType.APPLICATION_JSON_VALUE)
@ExposesResourceFor(Mission.class)
public class MissionRepresentation {
    private final MissionResource missionResource;
    private final UserResource userResource;

    public MissionRepresentation(MissionResource missionResource, UserResource userResource) {
        this.missionResource = missionResource;
        this.userResource = userResource;
    }

    // mapping
}

Answer 1

正如您所说，最好是实现一个连接表。那会是这样的:

create table mission_user (
    mission_id int,
    user_id int,
    primary key (mission_id, user_id)
)

然后 @ManyToMany 使用此表作为映射或实体，例如 MissionUser 并映射 User 和 Mission作为 @OneToMany 。