java - 使用集合加载 DTO

Question

@Entity
@Table(name = "person")
public class Consignment implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name = "person_id")
    private String personId;

    @Column(name = "person_name")
    private String personName;

    @OneToMany(fetch = FetchType.EAGER, mappedBy = "person")
    @Column(name = "cars_owned")
    private Set<Cars> casrsowned = new HashSet<>();
}

@Entity
@Table(name = "cars")
public class Cars implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

   @Column(name = "cars_id")
    private String carsId; 


  @ManyToOne
    @JoinColumn(name = "person")
    private Person person;

    @OneToOne
    private CarsDetail  carsDetail;
}

@Entity
@Table(name = "carsDetail")
public class CarsDetail implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name = "brand")
    private String brand;

    @Column(name = "color")
    private String color;

    @Column(name = "model")
    private String model;
}

class CarModelDTO {

    String personName;
    List<String> models;
}

在上面的关系中，想要返回CarModelDTO JPA查询where，

@Query("Select CarModelDTO(p.personName, p.casrsowned.carsDetail.model) from Person as p where p`enter code here`.id = :id"))
public CarModelDTO getCarmodelOwnedByAperson(@Param("id") Long id);

我尝试了多种方法，但它给出了 org.hibernate.QueryException:非法尝试取消引用集合

Answer 1

正如我已经描述过的 Retrieve List from repository interface to DTO list您应该执行以下步骤:

1. 首先使用您想要从查询输出返回的字段创建一个构造函数
2. 在查询中，您应该创建 dto 的新实例并将字段从数据库传递到新安装:

所以你需要这些改变:

1。在构造函数中:

您不应将列表用作 List<String> models;因为您应该将您的 dto 视为数据库的结果行。所以你需要有一个简单的 String model;

    public CarModelDTO (String name,String model){    
        this.name=name;
        this.model=model;   
    }

2。在@Query中:

• 您应该适本地使用多重内连接

• 您还应该将您的包名称附加到查询中的 CarModelDTO(这里我使用了 com.example，您应该更改它)

      @Query("Select com.example.CarModelDTO(p.personName, d.model ) from Person as p inner join p.carsowned c inner join c.carDetail d where p`enter code here`.id = :id")) 
      public CarModelDTO getCarmodelOwnedByAperson(@Param("id") Long id)