Question

我有2个简单的实体：学生和班级。我想发布一个学生，在其中指定其所属的班级，但是我陷入了休眠映射中。

ClassModel.class

@Entity
@Table(name = "class" )
public class ClassModel implements Serializable {


@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;

@NotEmpty
@Size(max = 20)
@Column(name = "name")
private String name;

@Column(name = "tables")
private int tables;

@Column(name = "chairs")
private int chairs;

@Column(name = "teacher")
private String teacher;
(getters + setters)

StudentModel

@Entity
@Table(name = "student")
public class StudentModel implements Serializable {

@Id
@Column(name = "student_id")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int student_id;

@NotEmpty
@Column(name = "name")
@Size(max = 50)
private String name;

@Column(name = "age")
private int age;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "id")
private ClassModel classModel;
(getters + setters)
}

StudentController.java

...
@Autowired
private StudentService studentService;

@Autowired
private ClassService classService;

@PostMapping(value = "/save")
public StudentModel save(@RequestBody StudentModel studentModel){
    ClassModel classModel = classService.findById(studentModel.getClassId()).get();
    studentModel.setClassModel(classModel);
    return studentService.save(studentModel);
}
...

但是当我向邮递员提出以下要求的请求时：

{
    "name": "some name",
    "age": 12,
    "class_id": 1
}

我从休眠中收到以下错误：

Column 'class_id' cannot be null

我的休眠映射在哪里出错？

Answer 1

这就是我在休眠状态下加入工作的方式。看看：

TrainingEntity.java

@Id
private Integer id;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "animal_id", nullable = false, insertable = false, updatable = false)
private AnimalEntity animalEntity;

@Column(name = "animal_id")
private Integer animalId;

AnimalEntity.java

@Id
private Integer id;

@OneToMany(mappedBy = "animalEntity", fetch = FetchType.LAZY)
private List<TrainingEntity> trainingEntityList = new ArrayList<>();

这是AnimalEntity和TrainingEntity之间的联接。 AnimalEntity有一个TrainingEntities列表。

Answer 2

错误在这一行：

"class_id": 1

您使用的是列名，而不是字段名。您必须将class_id替换为classModel，其中classModel是一个对象。其他解决方案是从json中按ID查找ClassModel，并将其设置为StudentModel的父项。

Hibernate无法将许多学生映射到一个班级

2 个答案: