休眠-有条件的加入

Question

I want to join 2 tables and do a query:
tableA with columns id, data
tableB with columns id, key

Say, I have one row in tablea:

id=5, data='xyz'

and two rows in tableb:

id=5, key='key1'
id=5, key='key2'

now I want to run the following SQL:

select * from tablea a left outer join tableb b on (a.id = b.id and b.key='key3')

which gets me a result with one row:

id=5, data='xyz', key=null

How can I do that with hibernateTemplate?

I tried with the following hibernate mapping file:

<hibernate-mapping package="de.xxx.vo">
<class name="zBean" table="TABLEA">
    <subselect>
        SELECT
            a.id, a.data
        FROM
            tablea a
            LEFT OUTER JOIN tableb b on a.id = b.id
    </subselect>

    <id name="id" column="ID" type="long"/>
    <property name="data" column="DATA" type="string" />
    <property name="key" column="KEY" type="string" />
</class>
</hibernate-mapping>

and this java-code-sniplet:

DetachedCriteria crit = DetachedCriteria.forClass(zBean.class)
    .add(Restrictions.eq("key", "key3"));
List<ListViewDataBean> result = hibernateTemplate.findByCriteria(crit);

That code generates a somewhat different SQL:

select * from tablea a left outer join tableb b on (a.id = b.id) where b.key='key3'

Answer 1

If you map 'tableB' as a OneToMany or OneToOne association in 'zBean', and use HQL instead of a Criteria query, you can use the 'with' clause:

select z from zBean z left join z.tableB b with b.key = 'key3'

Hibernate will generate the 'on' clause as you expect.