Question

我有两个实体类Activity和User。他们之间的关系是：

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

为了实现这一点，我在它们之间定义了@ManyToMany映射。以下是我的课程：

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;
    }
}

现在来自：

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

据我所知，@JoinColumn joinColumns的名称取一个实体的PK列名，而@JoinColumn的{{1}}名称取名为另一个实体的PK的列名。但在我的情况下，两个列名都相同，即来自inverseJoinColumns类的ID。

我的问题是如何避免列名冲突？任何建议都对我很有帮助。

Answer 1

在同一个表中有两个具有相同名称的列是没有意义的。所以只需为列选择一个不同的名称。

更改

@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"))

如该属性的名称所示，您提供的名称是连接列的名称，连接表的一部分，即列的名称将外键保存到活动或用户表中，在连接表ACTIVITY_USER中。 Hibernate已经知道用户和活动PK的名称：你在各自的@Id注释中告诉它。

Hibernate ManyToMany具有相同的JoinColumn名称

1 个答案: