使用Spring Boot/Hibernate关联Users、Technologies、Categories三张表咨询

你当前的实现存在3个核心错误：

• 关联关系映射错误：UserCategory 中未关联 TechnologyCategory 实体，仅存储分类名称，无法复用已存在的分类数据
• 级联策略配置不合理：未限制关联操作的级联范围，导致保存用户关联时触发分类的新增逻辑
• 实体关联方向错误：MyUser 中直接关联Category而非中间关联实体UserCategory，mappedBy配置错误导致外键关联失效，进而触发Hibernate建表异常

1. TechnologyCategory（技术分类实体） #

增加唯一约束避免分类名称重复，无需配置反向关联

@Entity
public class TechnologyCategory {
    @Id
    @SequenceGenerator(name = "id_seq", sequenceName = "id_seq", allocationSize = 1, initialValue = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "id_seq")
    private int id;
    
    @Column(name="name", unique = true, nullable = false)
    private String name;

    // 省略getter/setter
}

2. Technology（技术实体） #

保持原有基础配置即可，可根据需要添加和UserCategory的反向关联

@Entity
public class Technology {
    @Id
    @SequenceGenerator(name = "id_seq", sequenceName = "id_seq", allocationSize = 1, initialValue = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "id_seq")
    private int id;
    
    @Column(name = "name", unique = true, nullable = false)
    private String name;

    // 省略getter/setter
}

3. UserCategory（用户-分类关联实体） #

替换原有分类名称字段为TechnologyCategory实体关联，新增和MyUser的关联，配置合理的级联规则

@Entity
public class UserCategory {
    @Id
    @SequenceGenerator(name = "id_seq", sequenceName = "id_seq", allocationSize = 1, initialValue = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "id_seq")
    private int id;

    // 关联已有分类实体，不配置级联新增/更新，避免生成重复分类
    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "category_id", referencedColumnName = "id")
    private TechnologyCategory category;

    // 关联所属用户
    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "user_id", referencedColumnName = "id")
    private MyUser myUser;

    // 关联技术列表，配置多对多中间表
    @ManyToMany(fetch = FetchType.LAZY, cascade = {CascadeType.MERGE, CascadeType.PERSIST})
    @JoinTable(
        name = "user_category_technology",
        joinColumns = @JoinColumn(name = "user_category_id"),
        inverseJoinColumns = @JoinColumn(name = "technology_id")
    )
    private Collection<Technology> technologies;

    // 省略getter/setter
}

4. MyUser（用户实体） #

修改关联字段为UserCategory，配置正确的mappedBy属性

@Entity
public class MyUser {
    @Id
    @SequenceGenerator(name = "id_seq", sequenceName = "id_seq", allocationSize = 1, initialValue = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "id_seq")
    private int id;
    // 其他用户属性

    // 关联用户对应的分类绑定关系
    @OneToMany(mappedBy = "myUser", cascade = CascadeType.ALL, orphanRemoval = true)
    private Collection<UserCategory> userCategories;

    // 省略getter/setter
}

• 系统初始化阶段提前将10个固定分类存入TechnologyCategory表，后续所有分类关联均复用这10条已有数据
• 给用户创建分类关联时，必须先通过ID/名称从数据库查询已存在的TechnologyCategory对象，再关联到UserCategory，禁止直接new新的TechnologyCategory对象保存
• 如果技术也需要全局复用，保存技术时同样要先查询数据库是否存在对应记录，存在则复用，不存在再新增

内容的提问来源于stack exchange，提问作者NolanB