如何将内连接和左连接与JPQL和HQL结合起来

Question

我正在尝试实现一个HQL查询。我已经能够在SQL中实现它--我对它比较熟悉。我一直纠结于内部连接。

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，这就是我为HQL准备的。

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

这是可行的-除了我需要最后三行是一个左外连接而不是一个互斥的条件。我尝试过以多种方式实现这一点--但我总是遇到映射问题。

<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>

还有-我让它在SQL中工作，就像这样...

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子句中包含左联接条件，它将充当内联接。

如果item是可选的，那么item.parentItem也必须是可选的，所以您需要将其包含在左连接中。

尝试如下所示：

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'