解决 SpringData JPA 的n+1问题

1. 首先解决 n+1 问题

（1）Entity 添加 @NamedEntityGraph 

 1 @Entity
 2 @Table(name = "tb_depart_detail", schema = "")
 3 @NamedEntityGraph(name = "depart_detail.Graph", attributeNodes = {
 4         @NamedAttributeNode(value = "depart")
 5 })
 6 @SuppressWarnings("serial")
 7 public class DepartDetailEntity implements java.io.Serializable {
 8     @ManyToOne(fetch = FetchType.EAGER)
 9     @JoinColumn(name = "depart_id")
10     public DepartEntity getDepart() {
11         return depart;
12     }
13 
14     public void setDepart(DepartEntity depart) {
15         this.depart = depart;
16     }
17 }

（2） 重写 JpaRepository 的API 指定使用 NameEntityGraph

 1 import com.doctor.assistant.userserver.springdata.entity.DepartDetailEntity;
 2 import org.springframework.data.jpa.repository.EntityGraph;
 3 import org.springframework.data.jpa.repository.JpaRepository;
 4 
 5 import java.util.List;
 6 
 7 public interface DepartDetailRepository extends JpaRepository<DepartDetailEntity, String> {
 8 
 9     @Override
10     @EntityGraph(value = "depart_detail.Graph",type = EntityGraph.EntityGraphType.FETCH)
11     List<DepartDetailEntity> findAll();
12 }

（3） Test 测试 ：

2. 三层及更多关联时，解决 n+1 的方式：

 1 @Entity
 2 @Table(name = "t_base")
 3 @Inheritance(strategy = InheritanceType.JOINED)
 4 @NamedEntityGraph(name = "base.Graph", attributeNodes = {
 5         @NamedAttributeNode(value = "someList"),
 6         @NamedAttributeNode(value = "userList", subgraph = "outterGraph")
 7 }
 8 ,subgraphs = {
 9         @NamedSubgraph(name = "outterGraph",attributeNodes = {
10                 @NamedAttributeNode(value = "outterList",subgraph = "innerGraph")
11         }),@NamedSubgraph(name = "innerGraph",attributeNodes = {
12                 @NamedAttributeNode("innerList")
13         })
14 })

3. 若想保留原接口，再写一个 Repository的实现类，其中什么也不做，即可保留原方法：

1 @Repository
2 public interface EAGERUserRepository extends JpaRepository<TSBaseUser, String> {
3 }