java - 在Spring中创建多对一关系的对象(非空属性引用 transient 值)

Question

我正在尝试创建一个对象Activity，它是与类(class)多对一关系的一部分(一门类(class)可以有多个 Activity )。

当我尝试保留新的 Activity 对象时，出现以下错误:

org.hibernate.TransientPropertyValueException: Not-null property references a transient value - transient instance must be saved before current operation : app.model.activity.Activity.course -> app.model.Course

我将包含相关代码。

Controller POST方法

@RequestMapping(value = "/activities", method = RequestMethod.POST, consumes = MediaType.APPLICATION_JSON_UTF8_VALUE)
public @ResponseBody ResponseEntity<Void> createActivity(@Valid @RequestBody ActivityPostDto activityPostDto, UriComponentsBuilder ucBuilder) {

    CourseDto courseDto = courses.findById(activityPostDto.getCourseId());
    Course course = modelMapper.map(courseDto, Course.class);
    if (course==null){
        return new ResponseEntity(HttpStatus.BAD_REQUEST);
    }
    ActivityType activityType = activityService.findType(activityPostDto.getTypeId());
    if (activityType==null){
        return new ResponseEntity(HttpStatus.BAD_REQUEST);
    }

    Activity activity = new Activity();
    activity.setCourse(course);
    activity.setType(activityType);
    activity.setName(activityPostDto.getName());
    activity.setDate(new Date(activityPostDto.getDate()));
    activity = activityService.add(activity);

    HttpHeaders headers = new HttpHeaders();
    headers.setLocation(ucBuilder.path("/activities/{id}").buildAndExpand(activity.getId()).toUri());
    return new ResponseEntity<>(headers, HttpStatus.CREATED);
}

ActivityPostDto 类

public class ActivityPostDto implements Item {

   @NotNull
   private Long date;

   @NotNull
   private String name;

   @NotNull
   private Long courseId;

   @NotNull
   private Long typeId;

   ...

}

Activity 类别

public class Activity implements Item, Serializable {

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

   ...

   @ManyToOne
   @JoinColumn(name = "type_id", nullable = false)
   private ActivityType type;

   @ManyToOne
   @JoinColumn(name = "course_id", nullable = false)
   @JsonSerialize(using = CustomCourseSerializer.class)
   private Course course;

   ...
}

类(class)类别

public class Course implements Item, Serializable {

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

   ...

   @OneToMany(mappedBy = "course", fetch = FetchType.EAGER, targetEntity = Activity.class, cascade = CascadeType.ALL)
   @Fetch(value = FetchMode.SUBSELECT)
   @JsonSerialize(using = CustomActivityListSerializer.class)
   private List<Activity> activities;

   ...
}

我已经阅读了一些有关此问题的内容，但找不到解决方案。任何帮助将非常感激。谢谢。

Answer 1

看起来，类(class)不包含id。

你可以这样做:

// it can be changed to check existence of id
CourseDto courseDto = courses.findById(activityPostDto.getCourseId());
if (courseDto ==null){
    return new ResponseEntity(HttpStatus.BAD_REQUEST);
}

Course course = new Course();
course.setId(activityPostDto.getCourseId()) ;

Activity activity = new Activity();
activity.setCourse(course);
activity = activityService.add(activity);