这是我第一次使用spring和Dto，我试图创建两个，classes和student，我的问题是当我试图发送一个classes的get请求时，通常响应需要是与这个classe相关的name，numberS averageC和student，但我得到的是这个{“name”：“phonexe”，“numberS”：25，“averageC”：0.0，“学生”：null }学生列表总是空的，我在数据库中检查学生是否插入了classe_id，所以这不是问题这是我的实体

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    private Long id;
    private String codeM;
    private String firstName;
    private String lastName;
    @ManyToOne
    @JoinColumn(name = "classes_id")
    private Classes classes;
    @OneToMany(mappedBy = "student")
    private List<Notes> notes;
}

@Entity
@Data
@NoArgsConstructor(force = true)
@AllArgsConstructor
public class Classes {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    private long id;
    @NonNull
    @NotBlank(message = "First name must be filled")
    @Pattern(regexp = "^(?!\\s*$).+", message = "First name must not be blank or contain only spaces")
    private String name;
    @NonNull
    private Integer numberS;
    private double averageC=0.0;
    @OneToMany
    private List<Student> student;

}

这是我的Dto实体

@Data
public class StudentGetDto {
    @NotNull
    private String codeM;
    private String firstName;
    private String lastName;
    private ClassesGetDto classes;
    private List<NotesGetWithMatiereOnlyDto> notes;
}

@Data
public class ClassesGetDto {
    private String name;
    private Integer numberS;
    private Double averageC;
    private List<StudentGetDto> students;
}

这是控制器的功能

@GetMapping("/{Name}")
    public ClassesGetDto findByName(@PathVariable String Name) throws Exception{
        return modelMapper.map(classesService.findByName(Name), ClassesGetDto.class);
    }

modelMapper配置

@Configuration
public class ModelMapperConfig {

    @Bean
    public ModelMapper modelMapper() {
        return new ModelMapper();
    }
}