Question

I’m trying to convert the below SQL query to HQL and am having a few issues. A straight line by line conversion doesn’t work, I am wondering if I should be using an Inner Join in the HQL?

        SELECT (UNIX_TIMESTAMP(cosc1.change_date) - UNIX_TIMESTAMP(cosc2.change_date))          FROM customer_order_state_change cosc1           LEFT JOIN customer_order_state cos1_new on cosc1.new_state_id = cos1_new.customer_order_state_id           LEFT JOIN customer_order_state cos1_old on cosc1.old_state_id = cos1_old.customer_order_state_id           LEFT JOIN customer_order_state_change cosc2 on cosc2.customer_order_id = cosc1.customer_order_id           LEFT JOIN customer_order_state cos2_new on cosc2.new_state_id = cos2_new.customer_order_state_id           LEFT JOIN customer_order_state cos2_old on cosc2.old_state_id = cos2_old.customer_order_state_id          WHERE cos1_new.name = 'state1' AND  cos2_new.name = 'state2' and cosc2.change_date < '2008-11-06 09:00'  AND cosc2.change_date > '2008-11-06 06:00' GROUP BY cosc1.change_date, cosc2.change_date ; 

Query returns time in seconds between state changes for a customer order.

The state names and dates are dynamically inserted into the query.

Edit: Just tried this

'SELECT (UNIX_TIMESTAMP(cosc1.changeDate) - UNIX_TIMESTAMP(cosc2.changeDate))' +          ' FROM' +          ' ' + CustomerOrderStateChange.class.getName() + ' as cosc1' +         ' INNER JOIN ' + CustomerOrderStateChange.class.getName() +  ' as cosc2' +         ' WHERE cosc1.newState.name = ?' +         ' AND cosc1.order.id = cosc2.order.id' +          ' AND cosc2.newState.name = ?' +         ' AND cosc2.changeDate < ?' +         ' AND cosc2.changeDate > ?' +          ' GROUP BY cosc1.changeDate, cosc2.changeDate'; 

and received exception’outer or full join must be followed by path expression‘

Answer 1

Typically you HQL joins are specified using the property on the object, eg, if class Foo and Bar and Foo.bar is of type Bar, then from Foo f inner join f.bar as b is the join. As far as I know, there’s no way of performing a self-join in HQL (I could be wrong here).

That said, Hibernate allows you to write (slightly enhanced) SQL queries with session.createSQLQuery(...).