Hibernate ManyToMany 相同的 JoinColumn 名称

Question

我有两个实体类Activity和User. 它们之间的关系是：

• 一个人Activity可以有一个或多个User
• 一个User可以属于一个或多个Activity

所以为了实现这一点，我定义@ManyToMany了它们之间的映射。下面是我的课：

Activity：

@javax.persistence.Entity
@Table(name = "ACTIVITY")
public class Activity extends Entity {

    @Transient
    private static final long serialVersionUID = 4741665931936809028L;

    private Set<User> users;

    public Activity() {
        super();
    }

    @ManyToMany(targetEntity = User.class, cascade = { CascadeType.ALL })
    @JoinTable(name = "ACTIVITY_USER", joinColumns = @JoinColumn(name = "ID"), inverseJoinColumns = @JoinColumn(name = "ID"))
    public Set<User> getUsers() {
        return users;
    }

    public void setUsers(Set<User> users) {
        this.users = users;
    }
}

User：

@javax.persistence.Entity
@Table(name = "USER")
public class User extends Entity {

    @Transient
    private static final long serialVersionUID = -112950002831333869L;

    private Set<Activity> activities;

    public User() {
        super();
    }

    @ManyToMany(cascade = { CascadeType.ALL }, mappedBy = "users", targetEntity = Activity.class)
    public Set<Activity> getActivities() {
        return activities;
    }

    public void setActivities(Set<Activity> activities) {
        this.activities = activities;
    }
}

上述两个类都扩展了Entity：

@MappedSuperclass
public class Entity implements Serializable {

    @Transient
    private static final long serialVersionUID = 7470288121057059283L;

    private Long id;

    public Entity() {
        super();
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "ID", updatable = false, nullable = false, unique = true)
    public Long getId() {
        return id;
    }

    @SuppressWarnings("unused")
    private void setId(Long id) {
        this.id = id;
    }

    public void setLastUpdateTimestamp(Date lastUpdateTimestamp) {
        this.lastUpdateTimestamp = lastUpdateTimestamp;
    }


    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        return prime * result + ((getId() == null) ? super.hashCode() : getId().hashCode());
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }

        if (obj == null) {
            return false;
        }

        if (!getClass().equals(HibernateProxyHelper.getClassWithoutInitializingProxy(obj))) {
            return false;
        }

        final Entity other = (Entity) obj;

        if (getId() != other.getId()) {
            if (getId() == null) {
                return false;
            }
            if (!getId().equals(other.getId())) {
                return false;
            }
        }

        return true;
    }
}

现在从：

@JoinTable(name = "ACTIVITY_USER", joinColumns = @JoinColumn(name = "ID"), inverseJoinColumns = @JoinColumn(name = "ID"))

我明白的名称@JoinColumn中joinColumns带有一个实体的PK的列名，名之@JoinColumn的inverseJoinColumns需要一个实体的PK的列名。但在我的情况下，两个列名都是相同的，即ID来自Entity类。

我的问题是如何避免列名的这种冲突？任何建议都会对我很有帮助。

Answer 1

在同一个表中具有相同名称的两列是没有意义的。所以只需为列选择一个不同的名称。

改变

@JoinTable(name = "ACTIVITY_USER", 
           joinColumns = @JoinColumn(name = "ID"), 
           inverseJoinColumns = @JoinColumn(name = "ID"))

到

@JoinTable(name = "ACTIVITY_USER", 
           joinColumns = @JoinColumn(name = "ACTIVITY_ID"), 
           inverseJoinColumns = @JoinColumn(name = "USER_ID"))

正如属性名称所指示的那样，您在那里给出的名称是连接列的名称，连接表的一部分，即在连接表 ACTIVITY_USER 中保存活动或用户表的外键的列的名称。Hibernate 已经知道 User 和 Activity 的 PK 名称：你在它们各自的@Id注释中告诉过它。