springboot入门_数据库访问_jpa

Posted 2021-01-08 wlzq

本文记录使用jpa访问数据库。

创建spring boot项目，并在pom文件中添加相应的依赖包。

 1 <dependency>
 2             <groupId>org.springframework.boot</groupId>
 3             <artifactId>spring-boot-starter-data-jpa</artifactId>
 4         </dependency>
 5         <dependency>
 6             <groupId>org.springframework.boot</groupId>
 7             <artifactId>spring-boot-starter-web</artifactId>
 8         </dependency>
 9 
10         <dependency>
11             <groupId>mysql</groupId>
12             <artifactId>mysql-connector-java</artifactId>
13             <scope>runtime</scope>
14         </dependency>

在resources路径下创建yml文件，并配置数据库连接信息，JPA默认使用hibernate做的实现，所以也需要配置hibernate个别参数项，yml文件如下：

 1 spring:
 2   datasource:
 3     url: jdbc:mysql://localhost:3306/test
 4     username: root
 5     password: 123456
 6   jpa:
 7     show-sql: true
 8     hibernate:
 9       ddl-auto: update
10     database: mysql

创建实体类，与数据库表做映射

 1 @Entity
 2 @Table(name="t_city")
 3 public class City {
 4 
 5     @Id
 6     @GeneratedValue(strategy = GenerationType.AUTO)
 7     private Integer id;
 8     @Column(name = "city_code", length = 50)
 9     private String cityCode;
10     @Column(name = "city_name", length = 50)
11     private String cityName;
12     //省略get和set方法
13 }

创建dao接口，并继承JpaRepository

 1 @Repository
 2 public interface CityRepository extends JpaRepository<City, Long> {
 3 
 4     /**
 5      * 查询所有
 6      * @return
 7      */
 8     List<City> findAll();
 9 
10     /**
11      * 根据ID查询
12      * @param id
13      * @return
14      */
15     @Query("from City where id = :id")
16     City findById(@Param("id") Integer id);
17 
18     @Transactional
19     @Query("update City set city_name=?1 where city_code = ?2")
20     @Modifying
21     int update(String name, String code);
22 
23 }

创建一个service

 1 @Service
 2 public class CityService {
 3 
 4     @Autowired
 5     private CityRepository cityRepository;
 6 
 7     public int add(City city){
 8         Object obj = cityRepository.save(city);
 9         System.out.println(obj.toString());
10         return 1;
11     }
12 
13     public void delete(long id){
14         cityRepository.deleteById(id);
15     }
16 
17     public void update(String name, String code){
18         cityRepository.update(name, code);
19     }
20 
21     public List<City> findAllCity(){
22         return cityRepository.findAll();
23     }
24 
25     public City findById(Integer id){
26         return cityRepository.findById(id);
27     }
28 
29 }

创建controller，提供api方法测试

@RestController
@RequestMapping("data/jpa/city")
public class CityController {

    @Autowired
    private CityService cityService;

    @PutMapping
    public String add(@RequestBody City city){
        System.out.println(city.toString());
        cityService.add(city);
        return "success";
    }

    @DeleteMapping(value="/{id}")
    public String delete(@PathVariable String id){
        cityService.delete(Long.valueOf(id));
        return "success";
    }

    @PostMapping
    public String update(@RequestBody City city){
        cityService.update(city.getCityName(), city.getCityCode());
        return "success";
    }

    @GetMapping("/{id}")
    public City findById(@PathVariable("id") int id){
        City city = cityService.findById(id);
        return city;
    }

    @GetMapping("/list")
    public List<City> findAllCity(){
        List<City> cityList = cityService.findAllCity();
        return cityList;
    }

}

对于一般的增删改查方法，我们也可在再dao中继承CrudRepository来实现对应的方法。一般在开发中，我们的业务也会用到分页排序等功能，这JPA也做了支持，我们可以通过继承PagingAndSortingRepository来实现。