Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
678 views
in Technique[技术] by (71.8m points)

hibernate - HQL: How to select all entities distinct by some column?



A simple question:
In this example I need to retrieve all objects, but these objects must have distinct msgFrom fields.
When I use

List<Message> list = getHibernateTemplate().find("select distinct m.msgFrom from Message m WHERE msgTo = ? AND msgCheck = 0", dinc);

I get next error:

java.lang.ClassCastException: java.lang.Integer cannot be cast to com.example.model.Message

I suppose it's because Hibernate retrieves only one column, but I need an object, not column.
How can I do this?
I think that I can just scroll through a comma, i.e.

List<Message> list = getHibernateTemplate().find("select distinct m.msgFrom, m.To, m.datetime, .......... from Message m WHERE msgTo = ? AND msgCheck = 0", dinc);

But what if I have more than 20 fields here? Is there an easy solution?

Thanks!

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

You can also use Criteria and Projection together :

Criteria criteria = session.createCriteria( MyEntity.class );
criteria.setProjection( Projections.distinct( Projections.property( "id" ) ) );

Hope it help someone.


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...