Hibernate criteria query using Max() projection on key field and group by foreign primary key

I'm having difficulty representing this query (which works on the database directly) as a criteria query in Hibernate (version 3.2.5):

SELECT s.* 
  FROM ftp_status s 
 WHERE (s.datetime,s.connectionid) IN (SELECT MAX(f.datetime),
                                              f.connectionid 
                                         FROM ftp_status f
                                        GROUP BY f.connectionid);

so far this is what I've come up with that doesn't work, and throws a could not resolve property: datetime of: common.entity.FtpStatus error message:

Criteria crit = s.createCriteria(FtpStatus.class);
crit = crit.createAlias("connections", "c");
crit = crit.createAlias("id", "f");
ProjectionList proj = Projections.projectionList();
proj = proj.add(Projections.max("f.datetime"));
proj = proj.add(Projections.groupProperty("c.connectionid"));
crit = crit.setProjection(proj);
List<FtpStatus> dtlList = crit.list();

Here's the relevant reference configuration that Netbeans 6.8 generated directly from the database:

FtpStatus.hbm.xml -

<hibernate-mapping>
   <class name="common.entity.FtpStatus" table="ftp_status" catalog="common">
        <composite-id name="id" class="common.entity.FtpStatusId">
            <key-property name="siteid" type="int">
                <column name="siteid" />
            </key-property>
            <key-property name="connectionid" type="int">
                <column name="connectionid" />
            </key-property>
            <key-property name="datetime" type="timestamp">
                <column name="datetime" length="19" />
            </key-property>
        </composite-id>
        <many-to-one name="connections" class="common.entity.Connections" update="false" insert="false" fetch="select">
            <column name="connectionid" not-null="true" />
        </many-to-one>
        <many-to-one name="sites" class="common.entity.Sites" update="false" insert="false" fetch="select">
            <column name="siteid" not-null="true" />
        </many-to-one>
        <property name="upInd" type="boolean">
            <column name="up_ind" not-null="true" />
        </property>
        <property name="lastMessage" type="string">
            <column name="last_message" length="65535" not-null="true" />
        </property>
    </class>
</hibernate-mapping>

Connections.hbm.xml -

<hibernate-mapping>
    <class name="common.entity.Connections" table="connections" catalog="common">
        <id name="connectionid" type="java.lang.Integer">
            <column name="connectionid" />
            <generator class="identity" />
        </id>
        <property name="ip" type="string">
            <column name="ip" length="15" not-null="true" />
        </property>
        <property name="port" type="int">
            <column name="port" not-null="true" />
        </property>
        <property name="user" type="string">
            <column name="user" length="8" not-null="true" />
        </property>
        <property name="password" type="string">
            <column name="password" length="开发者_开发百科50" not-null="true" />
        </property>
        <set name="ftpStatuses" inverse="true">
            <key>
                <column name="connectionid" not-null="true" />
            </key>
            <one-to-many class="common.entity.FtpStatus" />
        </set>
    </class>
</hibernate-mapping>

I know I'm missing something, but my googling on hibernate hasn't revealed it yet. Alternatively a SQL query directly using s.createSQLQuery() or s.createQuery() is also acceptable, but I've had even less success writing that one.....

The Criteria you supplied seems to generate only the inner query part. You can combine the inner query e.g. by using DetachedCriteria:

DetachedCriteria maxDateQuery = DetachedCriteria.forClass(FtpStatus.class);
ProjectionList proj = Projections.projectionList();
proj.add(Projections.max("datetime"));
proj.add(Projections.groupProperty("connectionid"));
maxDateQuery.setProjection(proj);

Criteria crit = s.createCriteria(FtpStatus.class);
crit.add(Subqueries.propertiesEq(new String[] {"datetime", "connectionid"}, maxDateQuery));

List<FtpStatus> dtlList = crit.list();

Note that support for multicolumn subqueries is not implemented until in Hibernate 4.0.0.CR5 (HHH-6766).

As what comes to native SQL queries, Hibernate's createSQLString should work straight away with the query string you specified, or with the entities involved in the query added, if one want's to have explicit column names in the resulting query.

String queryString = "SELECT {status.*}"
                   + "  FROM ftp_status status"
                   + "  WHERE (datetime, connectionid) IN ("
                   + "    SELECT MAX(datetime), connectionid"
                   + "      FROM ftp_status"
                   + "      GROUP BY connectionid"
                   + "  )";

SQLQuery query = s.createSQLQuery(queryString).addEntity("status", FtpStatus.class);

List<FtpStatus> dtlList = query.list();