@ManyToOne JPA spring mysql 插入错误，列为空答案

【问题标题】：@ManyToOne JPA spring mysql insert error, column null@ManyToOne JPA spring mysql 插入错误，列为空
【发布时间】：2019-04-02 02:54:01
【问题描述】：

开始进入 Spring Boot 并使用 jpa 存储库来持久化本地 mysql 数据库，但插入时遇到问题。我将它简化为我的用户和任务类，用户可以有一个任务，我在任务类中使用@ManyToOne 注释进行一个方向映射。当在 post man 中调用端点时，我收到一个错误，并且跟踪表明 user_id 列为空（这是来自用户的映射列）。

为了调试，我在实际 taskRepo.save(task) 方法的任务服务类中设置了一个断点，看起来 user_id 实际上是。我尝试了通过选项映射的一对多和多对一的双向映射，但无济于事。

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

private Long postId;

@Column(unique = true, nullable = false)
private String username;

@Column(unique = true, nullable = false, name = "email")
private String email;

@Column(nullable = false)
private String password;





@Id
@GeneratedValue(strategy =GenerationType.IDENTITY)
@Column(name = "id", nullable = false)
private Long id;

@Column(name = "taskName", nullable = false)
private String taskName;

@Column(name = "description")
private String description;

@ManyToOne
@JoinColumn(name = "user_id", nullable = false)
private User user;






@Autowired
private TaskService taskService;

@GetMapping("/getAllTask")
public List<Task> getAllTasks(){
    return taskService.getAllTask();
}

@CrossOrigin(origins = "http://localhost:3000")
@PostMapping("/addTask")
public void addTask(@RequestBody Task task){
    taskService.addTask(task);
}



@Autowired
private TaskRepo taskRepo;

public List<Task> getAllTask(){
    List<Task> tasks = new ArrayList<>();
    taskRepo.findAll().forEach(task -> tasks.add(task));
    return tasks;
}

public void addTask(Task task){
    taskRepo.save(task);
}







{
        "taskName": "Task 1",
        "description": "This is the first item",
        "user_id": 1
    }



{
    "timestamp": "2019-04-02T02:15:06.989+0000",
    "status": 500,
    "error": "Internal Server Error",
    "message": "could not execute statement; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement",
    "path": "/task/addTask"
}

[enter image description here][1] ERROR 30016 --- [nio-8080-exec-3] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement] with root cause

java.sql.SQLIntegrityConstraintViolationException: Column 'user_id' cannot be null

【问题讨论】：

标签： java mysql hibernate jpa spring-data-jpa

【解决方案1】：

您的 json 格式不正确。 user_id 不是 Task 的字段。

您的 json 应该如下所示：

{
  "taskName": "Task 1",
  "description": "This is the first item",
  "user": {
    "id": 1
  }
}

userjson字段指的是

@ManyToOne
@JoinColumn(name = "user_id", nullable = false)
private User user;

而且因为User是一个对象，它需要被表示为一个JsonObject。

【讨论】：