springboot一对多查询

在SpringBoot中进行一对多查询的方法如下：

1.创建实体类

创建两个实体类实现一对多的关系，并在其中使用@OneToMany和@ManyToOne进行相应的注解。

2.创建DAO

创建两个DAO层，并在其中对应的实体类使用@ManyToMany和@OneToMany进行查询操作。

3.创建Service

创建对应的Service层，将两个DAO层进行整合，使其能够相互调用。

4.创建Controller

创建对应的Controller层，通过调用Service中的方法，获取数据并返回给前端页面。

示例代码：

//Student实体类
@Entity
@Table(name = "student")
public class Student {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private long id;

  @Column(name = "name")
  private String name;

  @OneToMany(mappedBy = "student", cascade = CascadeType.ALL)
  private List<Book> books = new ArrayList<>();

  //getter and setter
}

//Book实体类
@Entity
@Table(name = "book")
public class Book {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private long id;

  @Column(name = "name")
  private String name;

  @ManyToOne(cascade = CascadeType.ALL)
  @JoinColumn(name = "student_id")
  private Student student;

  //getter and setter
}

//StudentDAO
@Repository
public interface StudentDAO extends JpaRepository<Student, Long> {}

//BookDAO
@Repository
public interface BookDAO extends JpaRepository<Book, Long> {
  List<Book> findByStudentId(long studentId);
}

//StudentService
@Service
public class StudentService {

  private StudentDAO studentDao;
  private BookDAO bookDao;

  @Autowired
  public void setStudentDao(StudentDAO studentDao) {
    this.studentDao = studentDao;
  }

  @Autowired
  public void setBookDao(BookDAO bookDao) {
    this.bookDao = bookDao;
  }

  public List<Student> findAll() {
    return studentDao.findAll();
  }

  public List<Book> findBooksByStudentId(long studentId) {
    return bookDao.findByStudentId(studentId);
  }
}

//StudentController
@RestController
@RequestMapping("/students")
public class StudentController {

  private final StudentService studentService;

  @Autowired
  public StudentController(StudentService studentService) {
    this.studentService = studentService;
  }

  @GetMapping
  public List<Student> findAll() {
    return studentService.findAll();
  }

  @GetMapping("/{studentId}/books")
  public List<Book> findBooksByStudentId(@PathVariable long studentId) {
    return studentService.findBooksByStudentId(studentId);
  }
}

以上就是SpringBoot进行一对多查询的完整流程，通过以上步骤，就能够在SpringBoot中实现简单的一对多查询操作。