Question

我有三个实体：EntityA，EntityB和EntityC。从那些实体我需要通过使用spring数据jpa从Joining Query获取值到对象列表。查询是：

select x.id,x.formNo,x.name, z.testScore, y.semester 
   from  EntityA as x left join EntityB as z on x.id = z.a_id 
    inner join EntityC as y on x.c_id = y.id where x.id=1

实体是：

EntityA：

  @Entity
  public class EntityA {        
    @Id
    @GeneratedValue
    private Integer id;         
    private String name;        
    private String formNo;

    @OneToOne(mappedBy = "a",fetch=FetchType.LAZY, cascade = CascadeType.REMOVE)    
    private EntityB b;

    @ManyToOne
    @JoinColumn(name = "EntityC_id")
    private EntityC c;
}

EntityB：

@Entity
public class EntityB {

@Id
@GeneratedValue
private Integer id;     
private double testScore;

@OneToOne
@JoinColumn(name = "EntityA_id")
private EntityA a;  
}

EntityC：

@Entity
public class EntityC {
@Id
@GeneratedValue
private Integer id;     
private String semester;

@OneToMany(mappedBy = "c",fetch=FetchType.LAZY, cascade = CascadeType.REMOVE)
private List<EntityA> a;    
}

我试过这样的

@Repository
public interface SomeObjectRepository extends JpaRepository<Object, Integer>{   
public final static String FIND_WITH_QUERY 
    = "select x.id,x.formNo,x.name, z.testScore, y.semester 
   from  EntityA as x left join EntityB as z on x.id = z.a_id 
    inner join EntityC as y on x.c_id = y.id where x.id=:id";

    @Query(FIND_WITH_QUERY)
    public List<Object> getObjects(@Param("id") String id);
  }

Answer 1

您只需要意识到JPQL是一种与SQL不同的语言，并且可以学习它。 JPQL从不使用表名和列名。 JPQL连接依赖于实体之间的关联，而不依赖于ON子句。

因此查询应该只是

select x.id,x.formNo,x.name, z.testScore, y.semester
from EntityA x 
left join x.b z
inner join x.c y
where x.id = :id

Answer 2

JPQL 是一种与 SQL 不同的语言如果您不熟悉，可以使用原始 SQL 查询 我们调用Native Query

添加这一行到@Query，如下nativeQuery = true

@Repository
public interface SomeObjectRepository extends JpaRepository<Object, Integer>{   
public final static String FIND_WITH_QUERY 
    = "select x.id,x.formNo,x.name, z.testScore, y.semester 
   from  EntityA as x left join EntityB as z on x.id = z.a_id 
    inner join EntityC as y on x.c_id = y.id where x.id=:id";

    @Query(FIND_WITH_QUERY,nativeQuery = true)
    public List<Object> getObjects(@Param("id") String id);
  }

<块引用>

这将返回对象数组作为对象，您需要将其转换为数组

Object[] objArray = (Object[]) result_from_the_repositoryLayer;

如何通过使用spring数据jpa连接来从多个实体返回对象？

2 个答案: