Question

我刚开始玩NHibernate Linq，发现了一个奇怪的行为。我有一个类别和一个类产品。类别包含具有一对多关联的产品列表。这是映射：

  <class name="Category">
    <id name="Id">
      <generator class="hilo" />
    </id>
    <property name="Name" lazy="false" length="20" />

    <bag name="Products" cascade="none" lazy="false" inverse="true" fetch="join">
      <key column="CategoryId" />
      <one-to-many class="Product" />
      <!--<filter name="IdFilter" />-->
    </bag>
  </class>

  <class name="Product">
    <id name="Id">
      <generator class="hilo" />
    </id>
    <property name="Name" lazy="false" />
    <property name="Discontinued" lazy="false" />
    <property name="Price" lazy="false" />
    <many-to-one name="Category"
             class="Category"
             column="CategoryId"
             cascade="none" />
  </class>

当我使用此查询查询类别时

var cs = session.Query<Category>().Where(c => c.Products.Any(p => p.Price == 13.3392)).ToList();

我查看NHibernate profiler并查看此结果

select category0_.Id   as Id1_,
       category0_.Name as Name1_
from   Category category0_
where  exists (select products1_.Id
               from   Product products1_
               where  category0_.Id = products1_.CategoryId
                      and products1_.Price = 13.3392 /* @p0 */)

SELECT products0_.CategoryId   as CategoryId1_,
       products0_.Id           as Id1_,
       products0_.Id           as Id0_0_,
       products0_.Name         as Name0_0_,
       products0_.Discontinued as Disconti3_0_0_,
       products0_.Price        as Price0_0_,
       products0_.CategoryId   as CategoryId0_0_
FROM   Product products0_
WHERE  products0_.CategoryId = 131073 /* @p0 */

SELECT products0_.CategoryId   as CategoryId1_,
       products0_.Id           as Id1_,
       products0_.Id           as Id0_0_,
       products0_.Name         as Name0_0_,
       products0_.Discontinued as Disconti3_0_0_,
       products0_.Price        as Price0_0_,
       products0_.CategoryId   as CategoryId0_0_
FROM   Product products0_
WHERE  products0_.CategoryId = 32768 /* @p0 */

从数据库中逐个获取类别。因此，到数据库的往返量等于where子句匹配的类别对象的数量。

有没有办法告诉NHibernate优化查询？我完全迷失了。

非常感谢您的支持。

Answer 1

在您的行李映射课上

尝试添加batch-size

<bag name="Products" batch-size="25" ...>

NHibernate Linq。查询关联和多个SQL查询

1 个答案: