SpringDataJPA笔记(8)-EntityManager
SpringDataJPA笔记(8)-EntityManager
yingzi_code
发布于 2019-08-31 12:22:40
发布于 2019-08-31 12:22:40
EntityManager，以及union查询，left join查询
EntityManager是JPA中用于增删改查的接口，而通常我们使用的是Hibernate-EntityManager
Hibernate-EntityManager实现了标准的JPA，可以把它看成hibernate-core和JPA之间的适配器，它并不直接提供ORM的功能，而是对hibernate-core进行封装，使得Hibernate符合JPA的规范
使用案例
@ApiOperation(value = "查询", httpMethod = "GET")
@GetMapping("/search")
public List<CatView> search() {
Query query = entityManager.createNativeQuery("select id as id, name as name from cat_tb");
List<CatView> list = query.getResultList();
log.info("list: {}", JSON.toJSONString(list));
return list;
}
@ApiOperation(value = "查询union", httpMethod = "GET")
@GetMapping("/search/union")
public List<CatView> searchUnion() {
Query query = entityManager.createNativeQuery("select c.id as id, c.name as name from cat_tb c union all select d.id as id, d.name as name from dog_tb d");
List<CatView> list = query.getResultList();
log.info("list: {}", JSON.toJSONString(list));
return list;
}在使用JPA的时候，是不支持union查询的，只能使用原生sql查询，且在使用Query注解的时候无法使用普通类去接收查询的数据
使用Query注解方法
@Query(nativeQuery = true, value = "select c.id as id, c.name as name from cat_tb c union all select d.id as id, d.name as name from dog_tb d",
countQuery = "select count(*) from (select c.id as id from cat_tb c union all select d.id as id from dog_tb d) a")
<T> Page<T> findUnion(Pageable pageable, Class<T> type);使用普通类和接口类去接收查询数据
@ApiOperation(value = "union query查询", httpMethod = "GET")
@GetMapping("/left/union")
public Page<CatView> findUnion(@RequestParam int pageSize, @RequestParam int pageNum) {
Pageable pageable = PageRequest.of(pageNum, pageSize);
return catRepository.findUnion(pageable, CatView.class);
}
@ApiOperation(value = "union query查询2", httpMethod = "GET")
@GetMapping("/left/union2")
public Page<CatView2> findUnion2(@RequestParam int pageSize, @RequestParam int pageNum) {
Pageable pageable = PageRequest.of(pageNum, pageSize);
return catRepository.findUnion(pageable, CatView2.class);
}第一个方法会报错，第二个方法会得到正确的数据
第一个类是普通类
@Data
@AllArgsConstructor
public class CatView {
private Long id;
private String name;
}第二个是接口类
public interface CatView2 {
Long getId();
String getName();
}补充使用left join的案例，均得到正确的返回
@Query("select new com.mt.demo.jpa.entity.view.CatView(c.id , d.name) from CatEntity c left join DogEntity d on c.id = d.id")
<T> Page<T> findQuery(Pageable pageable, Class<T> type);
@Query("select c.id as id, d.name as name from CatEntity c left join DogEntity d on c.id = d.id")
<T> Page<T> findQuery2(Pageable pageable, Class<T> type); @ApiOperation(value = "left join query查询", httpMethod = "GET")
@GetMapping("/left/join")
public Page<CatView> leftJoin(@RequestParam int pageSize, @RequestParam int pageNum) {
Pageable pageable = PageRequest.of(pageNum, pageSize);
return catRepository.findQuery(pageable, CatView.class);
}
@ApiOperation(value = "left join query查询2", httpMethod = "GET")
@GetMapping("/left/join2")
public Page<CatView2> leftJoin2(@RequestParam int pageSize, @RequestParam int pageNum) {
Pageable pageable = PageRequest.of(pageNum, pageSize);
return catRepository.findQuery2(pageable, CatView2.class);
}本文参与 腾讯云自媒体分享计划，分享自作者个人站点/博客。
原始发表：2019年05月11日，如有侵权请联系 cloudcommunity@tencent.com 删除
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