SpringBoot嵌套保存实体触发PostgreSQL外键约束异常求助

嵌套保存包含子实体的Module时触发PostgreSQL外键约束错误：

org.postgresql.util.PSQLException: ERROR: insert or update on table violates foreign key constraint

单独保存各实体正常，但级联嵌套保存失败。相关实体代码、接口及请求JSON如下：

实体代码 #

@Entity(name = "question")
@NoArgsConstructor
@AllArgsConstructor
@Setter
@Getter
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
public class Question extends PersistableObject{
    @Id
    Long id;

    @OneToMany(fetch = FetchType.LAZY, cascade = { CascadeType.MERGE, CascadeType.PERSIST })
    @JoinColumn(name = "id")
    private List<Answer> answers = new ArrayList<>();

    Date created = new Date();

    private String description;


    @ManyToOne(fetch = FetchType.LAZY, cascade = { CascadeType.MERGE })
    @JoinColumn(name = "id", insertable = false, updatable = false)
    @JsonIgnore
    private Module module;
    //getters and setters
    // constructors
}

@Entity(name = "answer")
@NoArgsConstructor
@AllArgsConstructor
@Setter
@Getter
public class Answer extends PersistableObject {
    @ManyToOne
    @JoinColumn
    Question nextQuestion;

    @ManyToOne
    @JoinColumn(name = "id_question")
    Question prevQuestion;


    private Date created = new Date();

    @Basic
    private String description;

    @ManyToOne(fetch = FetchType.LAZY, cascade = { CascadeType.MERGE })
    @JoinColumn(name = "module", referencedColumnName = "id", insertable = false, updatable = false)
    private Module module;

}


@Entity(name = "module")
@NoArgsConstructor
@AllArgsConstructor
@Setter
@Getter
public class Module extends PersistableObject {

    String description;

    @OneToMany(fetch = FetchType.LAZY,mappedBy = "module",cascade = { CascadeType.MERGE, CascadeType.ALL })
    private List<Answer> answers = new ArrayList<>();

    @OneToMany(fetch = FetchType.LAZY,mappedBy = "module",cascade = { CascadeType.MERGE, CascadeType.ALL })
    private List<Question> questions = new ArrayList<>();

}

@MappedSuperclass
@Getter
@Setter
@EqualsAndHashCode
public abstract class PersistableObject extends RepresentationModel<PersistableObject> {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    Date created = new Date();

}

接口代码 #

@PostMapping("/")
public ResponseEntity<Module> create(@RequestBody Module module) {

    Module result = moduleService.save(module);

    URI uri = ServletUriComponentsBuilder.fromCurrentRequest()
            .path("/{id}")
            .buildAndExpand(result.getId())
            .toUri();

    return ResponseEntity
                .created(uri)
                .body(result);
}

请求JSON #

{
    "id": 1,
    "created": "2022-11-23T08:24:30.878+00:00",
    "description": "MDD",
    "answers": [
        {
            "id": 1,
            "created": "2022-11-23T08:24:30.878+00:00",
            "description": "AN1",
            "moduleId": 1
        },
        {
            "id": 2,
            "created": "2022-11-23T08:24:30.878+00:00",
            "description": "AN2",
            "moduleId": 1
        }
    ],
    "questions": [
        {
            "id": 1,
            "created": "2022-11-23T08:24:30.878+00:00",
            "answers": [
                {
                    "id": 3,
                    "created": "2022-11-23T08:24:30.878+00:00",
                    "description": "AN1",
                    "moduleId": 1
                },
                {
                    "id": 4,
                    "created": "2022-11-23T08:24:30.878+00:00",
                    "description": "AN2",
                    "moduleId": 1
                }
            ],
            "description": "Q1"
        }
    ]
}

解决方案 #

1. 修复外键映射错误 #

• Question与Module的关联：@JoinColumn(name = "id") 错误指向了Question自身的主键，应改为映射到Module的外键列（比如module_id），并移除insertable = false, updatable = false限制：

  @ManyToOne(fetch = FetchType.LAZY, cascade = { CascadeType.MERGE })
  @JoinColumn(name = "module_id")
  @JsonIgnore
  private Module module;
  

• Answer与Module的关联：insertable = false, updatable = false导致级联保存时无法写入外键值，同时规范列名为module_id：

  @ManyToOne(fetch = FetchType.LAZY, cascade = { CascadeType.MERGE })
  @JoinColumn(name = "module_id", referencedColumnName = "id")
  private Module module;
  

• Question与Answer的关联：@JoinColumn(name = "id")错误，应指向Answer表中关联Question的外键列（比如question_id）：

  @OneToMany(fetch = FetchType.LAZY, cascade = { CascadeType.MERGE, CascadeType.PERSIST }, orphanRemoval = true)
  @JoinColumn(name = "question_id")
  private List<Answer> answers = new ArrayList<>();
  

2. 维护双向关联引用 #

级联保存时，必须手动维护双向关联的双方引用，否则Hibernate无法正确写入外键。在moduleService.save方法中添加逻辑：

module.getQuestions().forEach(question -> {
    question.setModule(module);
    // 同时维护Question下Answer的关联
    question.getAnswers().forEach(answer -> {
        answer.setModule(module);
        answer.setPrevQuestion(question);
    });
});
module.getAnswers().forEach(answer -> answer.setModule(module));

3. 修正实体重复字段 #

Question和Answer类中重复定义了created字段，与父类PersistableObject的created冲突，直接移除子类中的该字段，统一使用父类的属性。

4. 调整请求JSON #

• 移除所有手动指定的id字段：实体主键是自增策略，由数据库自动生成，手动指定会导致主键冲突。
• 确保moduleId与实体属性映射：在Answer和Question的module属性上添加@JsonProperty("moduleId")注解，让Jackson能正确解析JSON中的字段。

5. 确认级联类型 #

Module类中对Question和Answer的级联使用CascadeType.ALL已经包含了持久化、更新等操作，无需额外调整，但建议添加orphanRemoval = true确保删除父实体时自动清理子实体。

内容的提问来源于stack exchange，提问作者Learner12