java - @ManyToOne @OneToMany Mapping ，外键为空

Question

@Entity
@Data
@NoArgsConstructor
public class Offer {
    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name = "user_id", referencedColumnName = "id")
    private User user;
}

@Data
@EqualsAndHashCode
@Entity
@NoArgsConstructor
public class User  {
    @OneToMany(mappedBy = "user",cascade = CascadeType.ALL,fetch=FetchType.LAZY)
    private Set<Offer> offers = new HashSet<Offer>();
}

请帮忙看看表 User 和 Offer .user_id 列中的映射是否正确......:(

Answer 1

我不确定这些是否只是实体的一部分，但为了使实体拥有一个 ID，您需要为其提供一个 ID，并将相关字段注释为 @Id。我还使用 @GenerateValue(strategy = GenerationType.IDENTITY) 所以每个表都会获得它自己的 id (由 Hibernate 生成，当您保存新实体而不是全局 id 时不提供 id，否则假设您添加一个提供，您获得值为 x 的 id，然后添加新用户，您获得值为 x+1 的 id 等等...

@Entity
@Data
@NoArgsConstructor
public class Offer {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name = "user_id", referencedColumnName = "id")
    private User user;

}



@Data
@EqualsAndHashCode
@Entity
@NoArgsConstructor
public class User  {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
   private long id;
     @OneToMany(mappedBy = "user",cascade = CascadeType.ALL,fetch=FetchType.LAZY)
    private Set<Offer> offers = new HashSet<Offer>();
}`