我用dto、entity创建了一个spring引导，也从dto生成了entity，反之亦然，但是当我试图获取数据时，数据没有存储在postgres sql中，它显示为null，但是首先创建的是controller类

import com.school.Entity.StudentDetails;
import com.school.Service.StudentService;
import com.school.dto.StudentDetailDto;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@RequestMapping("/api")
@CrossOrigin("*")
public class SchoolController {

    @Autowired
    StudentService studentService;

    @GetMapping("/test")
    public String test(){
        return "test";
    }
    @PostMapping("/uploadStudentData")
    public StudentDetailDto createStudentDetails(@RequestBody StudentDetailDto dto){
        return studentService.createStudentDetails(dto);
    }
    @GetMapping("/getAll")
    public List<StudentDetails> getAllStudentData(){
        return studentService.getAllStudentData();
    }
}

现在学生们开始上课了

import java.util.List;

public class StudentDetailDto {
    private Long id;
    private String branch;
    private List<StudentDto> student;

    //getter and setter
}

现在学生开始上课了

public class StudentDto {
    private Long id;
    private String firstName;
    private String lastName;
    private List<MarksListDto> marksList;
// getter and setter
}

现在是marks list类

public class MarksListDto {
    private Long id;
    private String subjectName;
    private Integer marks;
// getter and setter
}

现在是schooldetails实体类

@Entity
public class StudentDetails {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String branch;
    @OneToMany(targetEntity=Students.class, mappedBy="id", fetch=FetchType.EAGER,cascade=CascadeType.ALL)
    private List<Students> student;
//getter and setter
}

现在学生实体类

@Entity
public class Students {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String firstName;
    private String lastName;
    @OneToMany(targetEntity=MarksList.class, mappedBy="id", fetch=FetchType.EAGER,cascade=CascadeType.ALL)
    private List<MarksList> marksList;
//getter and setter
}

现在标记列表实体

@Entity
public class MarksList {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String subjectName;
    private int marks;
//getter and setter
}

存储库

public interface StudentRepository extends JpaRepository<StudentDetails, Long> {
}

现在最重要的是，我认为有什么问题是服务器

import com.school.Entity.StudentDetails;
import com.school.Repository.StudentRepository;
import com.school.dto.StudentDetailDto;
import org.modelmapper.ModelMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;

@Service
public class StudentService {
    @Autowired
    StudentRepository studentRepository;

    @Autowired
    ModelMapper modelMapper;

    public StudentDetailDto createStudentDetails(StudentDetailDto dto) {
        validateDto(dto);
        StudentDetails studentDetails = generateEntityFromDto(dto);
        studentDetails = studentRepository.save(studentDetails);
        return generateDtoFromEntity(studentDetails);
    }

    private StudentDetails generateEntityFromDto(StudentDetailDto dto) {
        StudentDetails studentDetails = modelMapper.map(dto, StudentDetails.class);
        return studentDetails;
    }

    private StudentDetailDto generateDtoFromEntity(StudentDetails studentDetails){
        StudentDetailDto dto = modelMapper.map(studentDetails,StudentDetailDto.class);
        return dto;
    }

    private void validateDto(StudentDetailDto dto) {

    }

//    public List<StudentDetailDto> getAllStudentData() {
//        List<StudentDetailDto> dto = new ArrayList<>();
//         studentRepository.findAll().forEach(dto::add);
//         return dto;
//    }
//    public String createStudentDetails(StudentDetails studentDetails){
//        studentRepository.save(studentDetails);
//        return "Student details created";
//    }
//
    public List<StudentDetails> getAllStudentData() {
        return new ArrayList<>(studentRepository.findAll());

    }
}

所以，当我在 Postman 中发送数据时，它向我显示它正在存储空值，我现在不知道，有人能帮我解决这个问题，能帮我把代码改进到最好的版本吗