Hibernate JPQL急切地获取元素

假设如下：

   @Query("SELECT new so.dto.CustomerWithTotal(s, sum(sb.amount)) from Customer s LEFT join fetch Bills sb ON sb.customer.sq=s.sq and sb.periodFrom <= ?3 and sb.periodTo >= ?2 WHERE s.department.sq=?1 group by s")
   List<CustomerWithTotal> findCustWithOrderTotal(Long departmentId, LocalDate from, LocalDate to);

我正试图把顾客连同他在特定时期内的订单总数一起拿来。但是，当我检查实际执行的查询时，我看到如下情况：

Hibernate: select customer.id as col_0_0_, sum(bill.amount) as col_1_0_ from customers...
Hibernate: select customer.id as cpx1_19_0_, customer.jpa_version as jpa_vers2_19_0_, ...
Hibernate: select customer.id as cpx1_19_0_, customer.jpa_version as jpa_vers2_19_0_, ...

---

Hibernate只在第一个查询中获取id，然后分别请求每个客户，从而产生N+1个查询。如何让Hibernate在第一次查询中急切地获取

customer

？最好不要在

CustomerWithBillTotal

？

中列出所有

customer

字段。如果要将实体别名传递给JPQL中的构造函数，Hibernate必须具体化完整的对象，因此它会在某个时间以某种方式获取所有字段。据我所知，如果传递实体别名，Hibernate中构造函数表达式的当前实现将始终传递代理，因此您看到的二次加载是由于Hibernate加载状态。如果只想获取实际需要的字段，则需要精确地列出它们

你可能也喜欢你所能提供的

我创建了这个库，以便在JPA模型和自定义接口或抽象类定义的模型之间进行简单的映射，类似于类固醇上的Spring数据投影。其思想是以您喜欢的方式定义目标结构（域模型），并通过JPQL表达式将属性（getter）映射到实体模型

在Blaze持久性实体视图中，您的用例的DTO模型可能如下所示：

@EntityView(Customer.class)
public interface CustomerWithBillTotal {
    @IdMapping("sq")
    Integer getId();
    String getCustomerName();
    // Other customer mappings you need...

    // Assuming you have a one-to-many association named "bills" in Customer
    @Mapping("COALESCE(SUM(bills.amount), 0)")
    // You can also use this if you don't have that association
    // @Mapping("COALESCE(SUM(Bills[customer.sq = VIEW(sq) AND periodFrom <= :periodFrom and periodTo >= :periodTo].amount), 0)")
    BigDecimal getAmount();
}

@EntityView(Customer.class)
public interface CustomerWithBillTotal {
    @IdMapping("sq")
    Integer getId();
    String getCustomerName();
    // Other customer mappings you need...

    // Assuming you have a one-to-many association named "bills" in Customer
    @Mapping("COALESCE(SUM(bills.amount), 0)")
    // You can also use this if you don't have that association
    // @Mapping("COALESCE(SUM(Bills[customer.sq = VIEW(sq) AND periodFrom <= :periodFrom and periodTo >= :periodTo].amount), 0)")
    BigDecimal getAmount();
}

   List<CustomerWithTotal> findByDepartmentId(Long departmentId, @OptionalParam("periodFrom") LocalDate from, @OptionalParam("periodTo") LocalDate to);