我正在 springdata jpa 的简单场景中尝试 EntityGraph：
这个想法只是获取一个带有 id 字段的实体并省略另一个名为 name 的字段。
这是要检索的实体：
Entity
@NamedEntityGraph(name = "Region.id",
attributeNodes = @NamedAttributeNode("id"))
public class Region {
@Id
public String id;
public String name;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
存储库：
public interface RegionRepository extends JpaRepository<Region, String>{
@EntityGraph(value = "Region.id")
Region findByRegionId(String name);
}
和服务：
@Service
public class RegionService {
@Autowired
private RegionRepository regionRepository;
public Region getRegion(String regionId) {
Region region = regionRepository.findByRegionId(regionId);
return region;
}
}
如前所述，检索整个区域。
我通过使用更多代码尝试了另一种方法。
添加了一个界面：
public interface RegionRepositoryCustom {
Region findByRegionId(String name);
}
并用它来添加一个 impl 类：
public class RegionRepositoryImpl implements RegionRepositoryCustom{
@PersistenceContext
private EntityManager em;
@Override
@Transactional
public Region findByRegionId(String id) {
EntityGraph<Region> entityGraph = (EntityGraph<Region>) em.getEntityGraph("Region.id");
Region region = em.createQuery("select r from Region r where r.id = :id", Region.class)
.setParameter("id", id)
.setHint("javax.persistence.fetchgraph", entityGraph)
.getSingleResult();
return region;
}
}
并尝试了这个变体：
public class RegionRepositoryImpl implements RegionRepositoryCustom{
@PersistenceContext
private EntityManager em;
@Override
@Transactional
public Region findByRegionId(String id) {
//EntityGraph<Region> entityGraph = em.createEntityGraph(Region.class);
//entityGraph.addAttributeNodes("id");
EntityGraph<Region> entityGraph = (EntityGraph<Region>) em.getEntityGraph("Region.id");
Map<String, Object> properties = new HashMap<>();
properties.put("javax.persistence.fetchgraph", entityGraph);
Region region = em.find(Region.class, id, properties);
return region;
}
}
还将 H2 与 application.properties 设置一起使用：
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true
spring.datasource.url=jdbc:h2:mem:AZ;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE;AUTO_RECONNECT=TRUE
spring.datasource.username=sa
spring.datasource.password=
spring.datasource.driver-class-name=org.h2.Driver
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.jpa.hibernate.ddl-auto=create-drop
spring.jackson.serialization.FAIL_ON_EMPTY_BEANS=false
这是 ide 控制台中使用的 SQL 模板：
Hibernate:
select
region0_.id as id1_0_,
region0_.name as name2_0_
from
region region0_
where
region0_.id=?
一切都没有奏效...
我错过了什么？