Question

I have a table called Gift, which has a one-to-many relationship to a table called ClickThrough – which indicates how many times that particular Gift has been clicked. I need to query for all of the Gift objects, ordered by ClickThrough count. I do not need the ClickThrough count returned, as I don’t need anything done with it, I just want to use it for purposes of ordering.

I need the query to return a List of Gift objects directly, just ordered by ClickThrough count. How do I do this using the Criteria API? I can find a lot of documentation out there on similar information to this, but nothing quite like what I need.

Answer 1

If you want to return a list of entities or properties in combination with a count you will need a group by. In criteria this is done through ProjectionList and Projections. e.g.

    final ProjectionList props = Projections.projectionList();
    props.add(Projections.groupProperty("giftID"));
    props.add(Projections.groupProperty("giftName"));
    props.add(Projections.count("giftID"), "count"); //create an alias for the count
    crit.setProjection(props);

    crit.add(Order.desc("count")); //use the count alias to order by

However, since you’re using ProjectionList you will also need to use AliasToBeanConstructorResultTransformer.