使用连接表

Question

我正在尝试使用 Java2EE 做一个类似 twitter 的项目，这是数据库的简单视图。
Mention、Followers和Following是三个JoinTable。 （请注意， said、follower、following 和每个用户字段都有 User.username 作为外键。） 我的第一个有问题，导致我的部署失败并出现以下异常：

异常描述：映射到元素[字段提及]的引用列名称[用户名]与映射引用上的有效字段不对应。

这是两个实体的映射。

推文：

public class Tweet implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @NotNull
    @Column(name = "id", nullable = false)
    private Integer id;

    ...

    @JoinColumn(name = "user", referencedColumnName = "username")
    @ManyToOne
    User user;
    @JoinTable(name = "Mention", joinColumns = {
        @JoinColumn(name = "tweet", referencedColumnName = "id")}, inverseJoinColumns = {
        @JoinColumn(name = "mentioned", referencedColumnName = "username")})
    @OneToMany
    private Collection<Tweet> mentions;

用户：

public class User implements Serializable {

    private static final long serialVersionUID = 1L;
    @Id
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 50)
    @Column(name = "username", nullable = false, length = 50)

    ...

    @OneToMany(mappedBy = "user")
    Collection<Tweet> tweets;
    @JoinTable(name = "Following", joinColumns = {
        @JoinColumn(name = "user", referencedColumnName = "username")}, inverseJoinColumns = {
        @JoinColumn(name = "following", referencedColumnName = "username")})
    @OneToMany
    Collection<User> following;
    @JoinTable(name = "Followers", joinColumns = {
        @JoinColumn(name = "user", referencedColumnName = "username")}, inverseJoinColumns = {
        @JoinColumn(name = "follower", referencedColumnName = "username")})
    @OneToMany
    Collection<User> followers;
    @OneToMany(mappedBy = "mentions")
    Collection<Tweet> mentioning;

我的映射出了什么问题？ 有人可以指出我的解决方案吗？

Answer 1

我认为您必须更改

@JoinColumn(name = "mentioned", referencedColumnName = "username")

以指定用户表，

@JoinColumn(name = "mentioned", referencedColumnName = "user")

因为基本上该消息是说您的 tweet 表没有外键字段 username ，但它不具有外键字段 username您已将其称为 user

这 -> 私人收藏提及； 也应该是一对多的用户集合

@OneToMany
@JoinTable(
    name = "Mention", 
    joinColumns = {
        @JoinColumn(name = "tweet", referencedColumnName = "id")
    }, 
    inverseJoinColumns = {
        @JoinColumn(name = "mentioned", referencedColumnName = "user")
    }
)    
private Collection<User> mentions;