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public void queryVnets(Page page) {
        StringBuffer hql = new StringBuffer();
        hql.append("select new Map(vn.id as id, vn.vnName as vnName, b.name as vnType, ");
        hql.append("vn.vnIptype as vnIptype, vn.vnIp as vnIp,vn.vnNat as vnNat, vn.vnFlag as vnFlag, ");
        hql.append("vn.vnetFlag as vnetFlag, (case when sum(vmvn.state)='0' then 0 else 1 end) as vnState, ");
        hql.append("vn.useType as useType, vn.createTime as createTime, ");
        hql .append("zone.oneName as oneName, zone.oneHypervisor as oneHypervisor, zone.oneSeq as oneSeq) ");
        hql.append("from VnetTable vn, ZoneTable zone, BridgeTable b ");
        hql.append("left join fetch vn.VnTables vmvn where zone.id = vn.zoneId and vn.vnType = b.id ");

... ...
        hql.append(" group by vn.id");
        if (vnState != null && !"".equals(vnState)) {
            if ("0".equals(vnState)) {
                hql.append(" having sum(vmvn.state)=0");
            } else if ("1".equals(vnState)) {
                hql.append(" having sum(vmvn.state)!=0");
            }
        }
    }

hbm配置文件：

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.base.mapping.VnetTable" table="vnet_table" >
        <id name="id" type="java.lang.String">
            <column name="ID" length="32" />
            <generator class="uuid.hex" />
        </id>
        <property name="vnId" type="java.lang.Long">
            <column name="VN_ID">
                <comment>創建虛擬網絡時得到的ID</comment>
            </column>
        </property>
...
        <property name="zoneId" type="java.lang.String">
            <column name="ZONE_ID" length="32">
                <comment>分區ID</comment>
            </column>
        </property>
        <property name="vlanId" type="java.lang.Integer">
            <column name="VLAN_ID">
                <comment>VLAN_ID</comment>
            </column>
        </property>
  <set name="vnTables" lazy="false" order-by="id asc" inverse="false" fetch="join" cascade="all">
            <key column="VN_NID"/>
            <one-to-many class="com.base.mapping.VnTable"/>
        </set>
    </class>
</hibernate-mapping>

理解inverse和cascade，可以參考：http://blog.csdn.net/wkcgy/article/details/6271321
總結：
<one-to-many>中，建議inverse=”true”，由“many”方來進行關聯關系的維護
<many-to-many>中，只設置其中一方inverse=”false”，或雙方都不設置
Cascade，通常情況下都不會使用。特別是刪除，一定要慎重。
操作建議
一般對many-to-one和many-to-many不設置級聯，這要看業務邏輯的需要;對one-to-one和one-to-many設置級聯。
many-to-many關聯關系中，一端設置inverse=”false”，另一端設置為inverse=”true”。在one-to-many關聯關系中，設置inverse=”true”,由多端來維護關系表

posted @ 2013-09-12 11:57 David1228 閱讀(16701) | 評論 (2) | 編輯收藏

Mysql中使用Join和In測試

-- 以下兩個查詢效率相當，查詢時間均為0.0xx秒，~ 但是Hibernate HQL不支持from后面接子查詢，可以直接使用SQL方式解決，ibatis當然可以用了。
SELECT count(*) from (
SELECT sum(t2.STATE) as vnSum, t1.ID FROM
vnetinfo_table t1, vm_vn_table t2
where t1.ID = t2.VN_NID and t1.ZONE_ID = '4028a49c3facdf26013fae12531b286e' GROUP BY t1.ID) t where t.vnSum = 0;

SELECT count(*) FROM vnetinfo_table v ,(
SELECT sum(t2.STATE) as vnSum, t1.ID as idd FROM
vnetinfo_table t1, vm_vn_table t2
where t1.ID = t2.VN_NID and t1.ZONE_ID = '4028a49c3facdf26013fae12531b286e' GROUP BY t1.ID) t
where v.ID = t.idd and t.vnSum = 0;

-- 查詢效率太低了，查詢時間均為0.5xx秒左右。要比以上兩個SQL耗時很多倍。~ Hibernate支持在where后用子查詢作為查詢條件。
SELECT count(*) FROM vnetinfo_table v WHERE v.id in
(SELECT CASE WHEN SUM(t2.STATE)=0 THEN t1.ID ELSE '' END
FROM vnetinfo_table t1, vm_vn_table t2
where t1.ID = t2.VN_NID and t1.ZONE_ID = '4028a49c3facdf26013fae12531b286e' GROUP BY t1.ID);

-- 使用join方式替換in 查詢時間均為0.09x秒左右。明顯提高了效率，但是Hibernate HQL任然不支持在這種聯合子查詢方式。
SELECT count(*) FROM vnetinfo_table v INNER JOIN (SELECT CASE WHEN SUM(t2.STATE)=0 THEN t1.ID ELSE '' END as idd
FROM vnetinfo_table t1, vm_vn_table t2
WHERE t1.ID = t2.VN_NID and t1.ZONE_ID = '4028a49c3facdf26013fae12531b286e' GROUP BY t1.ID) t ON v.ID = t.idd and t.idd IS not NULL;

附：Mysql中關于Exists用法的介紹請參見：http://www.nowamagic.net/librarys/veda/detail/639

posted @ 2013-08-21 13:47 David1228 閱讀(3764) | 評論 (2) | 編輯收藏

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