Question

我正在尝试实现HQL查询。我已经能够在SQL中实现它 - 我对它更熟悉一点。我一直挂着的是INNER JOINS。

这些类是这样实现的......

class Item

class Component extends Item
    private Item parentItem;

class Assembly extends Item

到目前为止，这就是我对HQL的看法......

SELECT
item.blah,
comp.blah,
assembly.blah
FROM
Component comp
LEFT OUTER JOIN comp.parentItem item,
Assembly assembly
WHERE 
item.parentItem = assembly

这是有效的 - 除了我需要最后三行是LEFT OUTER JOIN而不是互斥条件。我试图以多种方式实现这一点 - 但我一直在遇到映射问题。

<hibernate-mapping>
    <class lazy="false" name="com.kcp.common.domain.inventory.Item"
   table="W_INV_INV_ITEM" where="deleted=0">

       <joined-subclass lazy="false" name="com.kcp.common.domain.inventory.Component" table="W_INV_INV_COMPONENT">
         <key>
           <column name="ID">
               <comment>Primary and foreign key to W_INV_INV_ITEM.</comment>
            </column>
         </key>
         <many-to-one cascade="all" class="com.kcp.common.domain.inventory.Item" name="parentItem" outer-join="true">
              <column name="PARENT_ITEM_ID">
                <comment>Foreign key identifying the item to which this component is assembled.</comment>
              </column>
         </many-to-one>
       </joined-subclass>

        <joined-subclass lazy="false" name="com.kcp.common.domain.inventory.Assembly" table="W_INV_INV_MAJOR_ASSEMBLY">   
          <key>
            <column name="ID">
              <comment>Primary and foreign key to W_INV_INV_ITEM.</comment>
            </column>
          </key>
    </class>
 </hibernate-mapping>

另外 - 我让它像SQL一样工作......

FROM
DBO.W_INV_INV_ITEM item
INNER JOIN DBO.W_INV_INV_COMPONENT comp ON item.id = comp.id
LEFT OUTER JOIN DBO.W_INV_INV_ITEM parentInv ON comp.PARENT_ITEM_ID = parentInv.id
LEFT OUTER JOIN DBO.W_INV_INV_MAJOR_ASSEMBLY parentMA ON comp.PARENT_ITEM_ID = parentMA.id

Answer 1

如果在WHERE子句中包含LEFT JOIN条件，它将充当INNER JOIN。

如果item是可选的，那么item.parentItem也必须是可选的，因此您需要将其包含在LEFT JOIN中。

该HQL查询将生成可怕的SQL查询，您仍应优化它。

尝试这样的事情：

SELECT
    i.blah,
    c.blah
FROM Component c
LEFT JOIN c.parentItem i
LEFT JOIN i.parentItem p
WHERE 
    p is null or p.class = 'Assembly'



class Item

class Component extends Item
    private Item parentItem;

class Assembly extends Item

在HQL中实现多个JOINS

1 个答案: