JPA使用学习

1、添加相关jar包：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
 <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

2、添加配置文件：

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/test?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8&useSSL=true
    username: root
    password: root
    driver-class-name: com.mysql.cj.jdbc.Driver

3、添加实体类：

@Entity
public class User implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue
    private Long id;

    @Column(nullable = false, unique = true)
    private String name;

    @Column(nullable = false)
    private Integer age;

    @Column(nullable = false, unique = true)
    private String email;

    public User() {
        super();
    }

    public User(String name, Integer age, String email) {
        this.name = name;
        this.age = age;
        this.email = email;
    }
    
    ...........
    
}

4、实现Repository类：

public interface UserRepository extends JpaRepository<User, Long> {

    User findByName(String name);

    User findByNameOrEmail(String name, String email);
    
}

5、controller实现：

@Autowired
private UserRepository userRepository;

@RequestMapping("/getUsers")
public List<User> getUsers() {
    List<User> users=userRepository.findAll();
    return users;
}

6、多表联合查询：

@Query("select h.city as city, h.name as name, avg(r.rating) as averageRating "
        - "from Hotel h left outer join h.reviews r where h.city = ?1 group by h")
Page<HotelSummary> findByCity(City city, Pageable pageable);

@Query("select h.name as name, avg(r.rating) as averageRating "
        - "from Hotel h left outer join h.reviews r  group by h")
Page<HotelSummary> findByCity(Pageable pageable);

7、参考资料：

http://www.ityouknow.com/springboot/2016/02/03/spring-boot-web.html

http://www.ityouknow.com/springboot/2016/08/20/spring-boot-jpa.html