我們有時在進行開發過程中，使用jpa的@Query註解去選擇多張表然後返回一個DTO物件，這個時候我們需要特殊處理一下，因為預設情況下，你的jpa程式碼是不認DTO物件的。

參考文章：https://smarterco.de/spring-data-jpa-query-result-to-dto/

• entity實體

@Entity
@Getter
@Setter
@Builder
@ToString
@AllArgsConstructor
@NoArgsConstructor
public class OrderInfo extends EntityBase {
  @Id
  @GeneratedValue
  private int id;

  private int userId;

  private String userName;

  private double total;

  private String shippingName;

  private String shippingAddress;

  private Date orderTime;
}

@Entity
@Getter
@Setter
@Builder
@ToString
@AllArgsConstructor
@NoArgsConstructor
public class OrderItem extends EntityBase {
  @Id
  @GeneratedValue
  private int id;

  private int orderId;

  private int productId;

  private String productName;

  private int count;

  private double salePrice;
}
/**
 * DTO物件
 */
@Getter
@Setter
@Builder
@ToString
@AllArgsConstructor
@NoArgsConstructor
public class OrderList {
  public int id;

  private int userId;

  private String userName;

  private int productId;

  private String productName;

  private int count;

  private double salePrice;

}
 

• repository方法

  @Query("select new com.lind.microservice.productCenter.dto.OrderList" +
      "( o.id,o.userId,o.userName,oi.productId,oi.productName,oi.count,oi.salePrice) " +
      " from OrderInfo o " +
      " join OrderItem oi on o.id=oi.orderId")
  List<OrderList> getOrderInfos();

• 結果

[
{
"id": 5,
"userId": 3,
"userName": "lind",
"productId": 4,
"productName": "足球",
"count": 1,
"salePrice": 99
}
]