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我有三张桌子。Order, Location,保存多对多关系的表Order_Location在哪里。Order_Location

Order有List<Location>。Location有属性称为city. 使用 HQL（Java 的 Hibernate 3.6），我想获取特定订单的所有位置，按city.

在 hbm 文件中，List<Location>使用idbag进行映射。虽然我得到了 HQL，但生成的 SQL 查询有两次连接Location和Order_Location表，我觉得这是开销。

我在这里做错了什么？

SELECT o.locationList FROM Order o
join o.locationList locList  
where o.orderId = 1
order by locList.city desc

这转化为如下内容

select
  order4_.LOC_ID as order1_355_,
  order4_.LOC_CODE as order2_355_,
  order4_.CITY as order3_355_,
  order4_.CITY_LONG_NAME as order4_355_ 
from
   sche.order order0_ 
   inner join
   sche.order_location order1_ 
   on order0_.ORDER_ID=order1_.ORDER_ID 
   inner join
   sche.location order2_ 
   on order1_.LOC_ID=order2_.LOC_ID 
   inner join
   sche.order_location order3_ 
   on order0_.ORDER_ID=order3_.ORDER_ID 
   inner join
   sche.location order4_ 
   on order3_.LOC_ID=order4_.LOC_ID 
 where
   order0_.ORDER_ID=1 
 order by
   order2_.city desc

========= 编辑

Order.hbm.xml

  <?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"  

 >
<hibernate-mapping>
    <class name="collectionorderby.Order" table="ORDER">
        <id name="orderId" type="string">
            <column name="ORDER_ID" length="32" />
            <generator class="uuid" />
        </id>

        <idbag name="locationList" lazy="false" table="ORDER_LOCATION" fetch="select">
            <collection-id column="ORDER_LOCATION_ID" type="string">
                <generator class="uuid" />
            </collection-id>
            <key>
                <column name="ORDER_ID" length="32" not-null="true" />
            </key>
            <many-to-many column="LOC_ID" class="collectionorderby.Location"
                fetch="join" />
        </idbag>

    </class>
</hibernate-mapping>


Location.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<hibernate-mapping>
    <class name="collectionorderby.Location" table="LOCATION">
        <id name="locId" type="string">
            <column name="LOC_ID" length="50" />
        </id>

        <property name="locCode" type="string">
            <column name="LOC_CODE" length="50" />
        </property>
        <property name="city" type="string">
            <column name="CITY" length="50" />
        </property>
        <property name="cityLongName" type="string">
            <column name="CITY_LONG_NAME" length="500" />
        </property>

    </class>
</hibernate-mapping>

==== 编辑注意到，当我们提供时order by，翻译后的查询select从表的第一个实例获取，而order by使用表的第二个实例完成。我想，如果我们避免这些表的重复实例，这将不会发生。

4

1 回答 1

0

以下按预期工作。别名locList用于选择而不是o.locationList

SELECT locList  FROM Order o join o.locationList locList  where o.orderId = 1 order by locList.city desc
于 2013-07-31T12:13:08.763 回答