The com.mysema.query.group.GroupBy class provides aggregation functionality which can be used to aggregate query results in memory. Below are some usage examples.

Aggregating parent child relations

import static com.mysema.query.group.GroupBy.*;
   
Map<Integer, List<Comment>> results = query.from(post, comment)
    .where(comment.post.id.eq(post.id))
    .transform(groupBy(post.id).as(list(comment)));

This will return a map of post ids to related comments.

Multiple result columns

    
Map<Integer, Group> results = query.from(post, comment)
    .where(comment.post.id.eq(post.id))
    .transform(groupBy(post.id).as(post.name, set(comment.id)));

This will return a map of post ids to Group instances with access to post name and comment ids.

Group is the GroupBy equivalent to the Tuple interface.

More examples can be found here.