Spring boot jpa manytomany json 现在完全显示

Question

@Data
@Entity
@Table(name="course")

public class Course {

    @Id
    @GeneratedValue
    private Long id;
    private String title;
    private int credit;
    private String location;
    private String session;
    
    @ManyToMany(fetch = FetchType.LAZY,cascade = CascadeType.ALL, mappedBy="courses")
    @JsonIgnore
    private List<Student> students = new ArrayList<>();
    
    public void addStudent(Student student) {
        students.add(student);
    }
    
    public void removeStudent(Student student) {
        students.remove(student);
    }
}

@Data
@Entity
@Table(name="student")

public class Student {

    @Id
    @GeneratedValue
    private Long id;
    private String firstName;
    private String lastName;
    private String contactNumber;
    private int GPA;
    private String email;
    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinTable(name = "student_course",
        joinColumns = {@JoinColumn(name= "student_id")},
        inverseJoinColumns = {@JoinColumn(name="course_id")})
    
    private List<Course> courses = new ArrayList<>();
    
    public void addCourse(Course course) {
        courses.add(course);
    }
    
    public void removeCourse(Course course) {
        courses.remove(course);
    }
    
    
    
    
}

为了避免循环，我在 COURSE 一侧添加了@JsonIgnore，这使得 STUDENT 的输出看起来像这样：

 {
        "id": 7,
        "firstName": "Lil",
        "lastName": "Dogg",
        "contactNumber": "002002",
        "email": "lil@yahoo.com",
        "courses": [
            {
                "id": 2,
                "title": "M103",
                "credit": 3,
                "location": "Lab30",
                "session": "10:00"
            }
        ],
        "gpa": 2
    }

没关系。但在 COURSE 中，输出如下所示：

 {
        "id": 1,
        "title": "M105",
        "credit": 2,
        "location": "Lab50",
        "session": "08:00"
    },
    {
        "id": 2,
        "title": "M103",
        "credit": 3,
        "location": "Lab30",
        "session": "10:00"
    },

它省略了private List<Student> students = new ArrayList<>();！

它没有显示在 Json 输出中！...当我在 Student 端添加 @JsonIgnore 时...它省略了 private List<Course> courses = new ArrayList<>();，如上所示！

如何解决？

Answer 1

不要在控制器中将实体类呈现为 JSON 响应。相反，创建单独的DTO 类CourseDTO 和StudentDTO，您只需将所需的数据放入响应中并返回它们：

@GetMapping
public StudentDTO getStudent() {