Hibernate criteria order by one-to-many association count

Question

I have an entity "X" with a one-to-many association to "Y"s

Each X has a unique xid, and each Y has an xid, and a unique yid

I want to write a criteria that produces a list of X's ordered by the number of associated Y's

Here is the equivalent SQL

SELECT * 
FROM X JOIN Y ON X.xid = Y.xid
GROUP BY X.xid
ORDER BY COUNT(Y.yid) DESC

How do I express this using Hibernate Criteria?

Many thanks Peter

Answer 1

You'll want to create an alias for the Y collection, get its count, and sort by it. Here is an example:

// Create the criteria assuming session is open
Criteria criteria = session.createCriteria(X.class, "x");

// Give the Y association an alias
criteria.createAlias("x.yCollectionName", "yCollectionAlias"); 

// Get the count of IDs in the joined collection
criteria.setProjection(Projections.projectionList().add(Projections.groupProperty("yCollectionAlias.id"))
.add(Projections.count("yCollectionAlias.id").as("yCollectionAliasCount")));

// Sort the criteria associated by Ys
criteria.addOrder(Order.desc("yCollectionAliasCount"));