@Entity                  /*用于标注该类对应数据库的表*/                          @Entity 
@Table(name = "users")   /*用于映射表名和实体类名*/                              public class Detail {
public class User {                                                                  @Id
    @Id                  /*用于标注该字段为User类中的主键*/                            @GeneratedValue
    @GeneratedValue      /*用于标注主键的生成策略*/                                    private long id;
    private long id;                                                                  private String position;
    private String name;                                                              private String phoneNumber;   //驼峰
    private int age;                                                                  @Column(name = "education")
    private String description;                                                       private String edu;  
}     /*省略getter、setter方法*/                                                 }       //省略getter、setter方法     

@Repository         //用于标注数据库访问组件（也可不写，Spring Boot也可正常工作）
public interface UsersRepository extends JpaRepository<User,Long> {    //用于操作数据库"users"表
}

public List<User> singleSort(){     //单属性排序
    return usersRepository.findAll(Sort.by(Sort.Direction.ASC, "id"));
}

public List<User> multiSort() {    //多属性排序
    Sort.Order idOrder = Sort.Order.asc("id");
    Sort.Order ageOrder = Sort.Order.desc("age");
    return usersRepository.findAll(Sort.by(idOrder, ageOrder));  //先按id升序再按age降序进行排序
}

public List<User> page(int pageNum, int pageSize){              //pageNum表示第几页，pageSize表示每页有几条数据
    Sort sort = Sort.by(Sort.Direction.ASC, "id");              //根据id进行排序
    PageRequest pageRequest = PageRequest.of(pageNum, pageSize, sort);
    Page<User> userPage = usersRepository.findAll(pageRequest);
    return userPage.getContent();                               //getContent()方法可获取查询结果，
}                                                               //实际情况下至少还需返回查询总数：userPage.getTotalElements()

@Repository
public interface UsersRepository extends JpaRepository<User,Long> {
    User findByNameAndAge(String name, int age);
    List<User> readByAgeLessThanEqual(int age);
    List<User> queryByNameStartingWith(String word);
    List<User> getByDescriptionIsNotNull();

    @Transactional
    @Modifying
    int deleteByName(String name);    

    List<User> findByAge(Sort sort);             //约定方法排序。方法名findByAge后加"BySort"会报错

    Page<User> findByAge(Pageable pageable);     //约定方法分页。方法名findByAge后加"ByPageable"会报错
}

public interface UsersRepository extends JpaRepository<User,Long> {
    @Query("SELECT u from User u where u.name = ?1 and u.age = ?2")       //"?1"代表第一个参数，"?2"代表第二个参数，以此类推。
    User findByNameAndAge(String name, int age);

    @Query("select u from User u where u.name = :myName and u.age = :myAge")         //":参数名"的方式指定方法中的参数
    User findByNameAndAge(@Param("myName") String name, @Param("myAge") int age);    //使用@Param注解注入参数
}

public interface UsersRepository extends JpaRepository<User,Long> {
    @Query(value = "SELECT * from users where name= ?1", nativeQuery = true)   //value中为普通的sql语句
    User findByName(String name);
}     //也可使用@Param注解来注入参数，此处未写出

@Query("select u from User u where u.age = ?1")
List<User> findByAge(int age, Sort sort);           //自定义方法的排序

@Query("select u from User u where u.age = ?1")
Page<User> findByAge(int age, Pageable pageable);   //自定义方法的分页

public List<User> sortByLength(int age) {
    JpaSort sort = JpaSort.unsafe(Sort.Direction.ASC, "LENGTH(name)");     //LENGTH(属性名)。必须使用JpaSort.unsafe，使用Sort.by()报错
    return usersRepository.findByAge(age, sort);
}

@Query(value = "SELECT * from users where age= ?1", nativeQuery = true)
User findByName(int age);

 @Query("SELECT u from users u where u.name = ?1 and u.age = ?2")  //无法识别users。hql操作实体类，而不是数据库表（应是User类，而不是users表）
 User findByNameAndAge(String name, int age);
 
 @Query("SELECT * from User where name = ?1 and age = ?2")            //hql不支持"*"写法  
 User findByNameAndAge(String name, int age);
 
 @Query("SELECT User from User u where u.name = ?1 and u.age = ?2")   //启动时报一个空指针错误(It confuses me)
 User findByNameAndAge(String name, int age);

@Component
public class UsersService {

    @Resource                                     //推荐使用@Resource，不推荐@Autowired(具体原因自行google)
    private UsersRepository usersRepository;

    /**
    * 使用默认方法 - 新增或更新一条数据
    */
    public User saveUser(User user) {
        return usersRepository.save(user);
    }

    //...
}

@RestController
@RequestMapping("/user")
public class UsersController {

    @Resource
    private UsersService usersService;

    @RequestMapping("/all")
    public List<User> getAllUsers() {
        return usersService.getAllByDefault();
    }

    //类似调用UsersService中方法即可
    //...
}