java - 休眠自我加入多对多与额外的列

Question

帮助我了解如何使用休眠实现多对多自连接和额外的列？我也应该映射连接表吗？或者可能以另一种方式存在？我找不到任何对我有用的东西......

Answer 1

将连接表映射为专用实体，然后通过两个OneToMany关系链接它。这通常是正确的方法，因为一旦您添加更多列，它就不仅仅是技术细节。

对于自联接，这应该以相同的方式工作，您在该模型上只有两个与联接实体关联的字段。

请参阅此答案，其中对此进行了更详细的描述。

Answer 2

这个问题我纠结了很久，也许有人会觉得 Wolfram 的措辞很难，所以我会更详细地解释一下：想象一下，我们需要什么 map 之类的uml_diagramm

我需要在任意两个用户之间建立链接，这些链接用于他们之间的聊天。所以我们的用户类将是：

@AllArgsConstructor
@NoArgsConstructor
@Builder
@Data
@Entity
public class User  implements Serializable {
    private String email;
    private String password;
    private Long id;
    private String nickname;
    private String phone;
    private Collection<Chats> chatsById;
    private Collection<Chats> chatsById_0;


@Basic
@Column(name = "email", nullable = false, length = -1)
public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

@Basic
@Column(name = "password", nullable = false, length = -1)
public String getPassword() {
    return password;
}

public void setPassword(String password) {
    this.password = password;
}

@Id
@Column(name = "id", nullable = false)
public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

@Basic
@Column(name = "nickname", nullable = true, length = -1)
public String getNickname() {
    return nickname;
}

public void setNickname(String nickname) {
    this.nickname = nickname;
}

@Basic
@Column(name = "phone", nullable = true, length = -1)
public String getPhone() {
    return phone;
}

public void setPhone(String phone) {
    this.phone = phone;
}

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    User user = (User) o;
    return Objects.equals(email, user.email) && Objects.equals(password, user.password) && Objects.equals(id, user.id) && Objects.equals(nickname, user.nickname) && Objects.equals(phone, user.phone);
}

@Override
public int hashCode() {
    return Objects.hash(email, password, id, nickname, phone);
}


@OneToMany(mappedBy = "userByIdFrom")
public Collection<Chats> getChatsById() {
    return chatsById;
}

public void setChatsById(Collection<Chats> chatsById) {
    this.chatsById = chatsById;
}

@OneToMany(mappedBy = "userByIdTo")
public Collection<Chats> getChatsById_0() {
    return chatsById_0;
}

public void setChatsById_0(Collection<Chats> chatsById_0) {
    this.chatsById_0 = chatsById_0;
}

}

请注意两个 @OneToMany 注释 - getChatsById 和 getChatsById_0

现在我们的聊天类：

@AllArgsConstructor
@NoArgsConstructor
@Builder
@Data
@Entity
@IdClass(ChatsPK.class)
public class Chats implements Serializable {
    private Long idFrom;
    private Long idTo;
    private Object uuid;
    private User userByIdFrom;
    private User userByIdTo;

@Id
@Column(name = "id_from", nullable = false)
public Long getIdFrom() {
    return idFrom;
}

public void setIdFrom(Long idFrom) {
    this.idFrom = idFrom;
}

@Id
@Column(name = "id_to", nullable = false)
public Long getIdTo() {
    return idTo;
}

public void setIdTo(Long idTo) {
    this.idTo = idTo;
}

@Basic
@Column(name = "uuid", nullable = false)
public Object getUuid() {
    return uuid;
}

public void setUuid(Object uuid) {
    this.uuid = uuid;
}

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    Chats chats = (Chats) o;
    return Objects.equals(idFrom, chats.idFrom) && Objects.equals(idTo, chats.idTo) && Objects.equals(uuid, chats.uuid);
}

@Override
public int hashCode() {
    return Objects.hash(idFrom, idTo, uuid);
}

@ManyToOne
@JoinColumn(name = "id_from", referencedColumnName = "id", nullable = false)
public User getUserByIdFrom() {
    return userByIdFrom;
}

public void setUserByIdFrom(User userByIdFrom) {
    this.userByIdFrom = userByIdFrom;
}

@ManyToOne
@JoinColumn(name = "id_to", referencedColumnName = "id", nullable = false)
public User getUserByIdTo() {
    return userByIdTo;
}

public void setUserByIdTo(User userByIdTo) {
    this.userByIdTo = userByIdTo;
    }
}

老实说，我自己还没有弄清楚为什么它会起作用，但是应该有更多的细节

同时，我知道 intelijIdea 可以从数据库中为您生成模型，这可能有助于您通过 Database Schema - Entity Class 的详细设置生成持久性映射。（此代码由它生成）