Spring Data JPA @OneToMany映射保存时出现StackOverflowError求助

我正在学习Spring Boot，有GYMS和HOURS两张数据表，在Gym实体中声明了@OneToMany映射，Hours实体中声明了@ManyToOne映射，但保存新健身房及其营业时间到数据库时出现StackOverflowError，求解决办法，谢谢！

数据表结构 #

CREATE TABLE gyms (
  id int NOT NULL AUTO_INCREMENT,
  name varchar(60) NOT NULL,
  address varchar(255),
  city varchar(255),
  province varchar(3),
  postal_code char (7),
  phone_number varchar(20),
  PRIMARY KEY (id)
);

CREATE TABLE hours (
  id int NOT NULL AUTO_INCREMENT,
  gym_id int NOT NULL,
  day_of_week INT,
  opening_time TIME,
  closing_time TIME,
  PRIMARY KEY (id),
  FOREIGN KEY (gym_id) REFERENCES gyms(id)
);

Gym实体类 #

@Entity
@Table (name = "gyms")
@NoArgsConstructor
@Getter
@Setter
public class Gym {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    private String name;
    private String address;
    private String city;
    private String province;
    private String postalCode;
    private String phoneNumber;

    @OneToMany(mappedBy = "gym", cascade = CascadeType.ALL)
    private List<Hours> hours;

    public Gym(String name, String address, String city, String province, String postalCode, String phoneNumber) {
        this.name = name;
        this.address = address;
        this.city = city;
        this.province = province;
        this.postalCode = postalCode;
        this.phoneNumber = phoneNumber;
    }
}

Hours实体类 #

@Entity
@Table (name = "hours")
@NoArgsConstructor
@Getter
@Setter
public class Hours {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "gym_id")
    private Gym gym;

    private int dayOfWeek;
    private Time openingTime;
    private Time closingTime;
    
    public Hours(int dayOfWeek, String openingTime, String closingTime) {
        this.dayOfWeek = dayOfWeek;
        this.openingTime = Time.valueOf(openingTime);
        this.closingTime = Time.valueOf(closingTime);
    }
}

GymService类 #

@Service
public class GymService {
    private final GymRepository gymRepository;
    private final HoursRepository hoursRepository;
    
    @Autowired
    public GymService(GymRepository gymRepository, HoursRepository hoursRepository) {
        this.gymRepository = gymRepository;
        this.hoursRepository = hoursRepository;
    }

    public Gym addNewGym(Gym gym, List<Hours> hours) {
        gym.setHours(hours);
        for (Hours hour : hours) {
            hour.setGym(gym);
        }
        return gymRepository.save(gym);
    }

}

出现StackOverflowError的核心原因是双向关联实体间的循环引用：Lombok默认生成的toString()（部分IDE或Lombok配置会自动添加）会包含关联字段，导致调用Gym.toString()时遍历hours列表，每个Hours.toString()又会调用关联的Gym.toString()，无限循环直到栈溢出。

解决步骤： #

1. 排除关联字段的toString生成
   在实体类上添加@ToString注解，明确排除互相引用的字段：

   // Gym类修改
   @Entity
   @Table(name = "gyms")
   @NoArgsConstructor
   @Getter
   @Setter
   @ToString(exclude = "hours")
   public class Gym {
       // 原有代码不变
   }
   

   // Hours类修改
   @Entity
   @Table(name = "hours")
   @NoArgsConstructor
   @Getter
   @Setter
   @ToString(exclude = "gym")
   public class Hours {
       // 原有代码不变
   }
   

2. 同步处理equals和hashCode
   若Lombok自动生成了equals/hashCode方法，同样需要排除关联字段避免循环：

   // Gym类添加
   @EqualsAndHashCode(exclude = "hours")
   // Hours类添加
   @EqualsAndHashCode(exclude = "gym")
   

3. 验证保存逻辑
   你的GymService保存逻辑是正确的：双向关联关系已正确建立，CascadeType.ALL能实现级联保存，无需修改。

额外建议 #

• 双向关联中@OneToMany使用mappedBy是正确做法，避免双向维护外键导致数据不一致；
• @ManyToOne上的FetchType.LAZY是默认值，显式声明有助于提升查询性能，避免不必要的关联数据加载。

内容的提问来源于stack exchange，提问作者developerron