Question

Sample database table:

1. ID = 1, msgFrom = ‘Hello’, foobar = ‘meh’
2. ID = 2, msgFrom = ‘Goodbye’, foobar = ‘comments’
3. ID = 3, msgFrom = ‘Hello’, foobar = ‘response’

Sample desired output (generated by hibernate query):

1. ID = 1, msgFrom = ‘Hello’, foobar = ‘meh’
2. ID = 2, msgFrom = ‘Goodbye’, foobar = ‘comments’

In the above example, the third record would be excluded from the results since the msgFrom column is the same. Let’s say the Java/Hibernate class is called Message. I would like the results to be returned as a list of Message objects (or Objects that can be cast to Message, anyway). I want to use the Criteria API if possible. I saw this example on SO and it seems similar but I cannot implement it correctly as of yet.

 select e from Message e 
    where e.msgFrom IN (select distinct m.msgFrom 
                          from Message m
                          WHERE m.msgTo = ? 
                          AND m.msgCheck = 0");

The reason I am doing this is to have the filtering of distinct records done on the database, so I am not interested in answers where I have to filter anything on the application server.

edit: Article showing basically what I want to do. http://oscarvalles.wordpress.com/2008/01/28/sql-distinct-on-one-column-only/

Answer 1

Please try this and let me know

DetachedCriteria msgFromCriteria = DetachedCriteria.forClass(Message.class);
ProjectionList properties = Projections.projectionList();
properties.add(Projections.groupProperty("messageFrom"));
properties.add(Projections.min("id"),"id");
msgFromCriteria.setProjection(properties);

Criteria criteria = s.createCriteria(Message.class);
criteria.add(Subqueries.propertiesIn(new String[]{"messageFrom","id"}, 
    msgFromCriteria));
List<Message> list = criteria.list();

for(Message message:list){
    System.out.println(message.getId()
        +"-------"
        +message.getMessageFrom()
        +"-----"
        +message.getFoobar());
}