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

Question

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

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Answer 1

Try this, it worked for me:

SELECT FROM YourTableName 
WHERE somecolumnName=condition 
GROUP BY yourDistinctColumnName

Answer 2

Hibernate criteria is pretty easy to select distinct results. If you want single result to be returned in the projected result, you may want to use:

Criteria criteria = session.createCriteria(Message.class);
criteria.setProjection(Projections.distinct(Projections.property("msgFrom ")));
List<String> msgFromList = criteria.list();

If you want the result to include entire Message class with all its property set, you can use Hibernate result Transformer,

Criteria criteria = session.createCriteria(Message.class);
criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
List<Message> messages = criteria.list();

But it filters on the basis of root entity.

Or

Criteria criteria = session.createCriteria(Message.class);

ProjectionList projection = Projections.projectionList();
projection.add(Projections.distinct(Projections.property("msgFrom")));
//Add as many columns as you want using Projection
projection.add(Projections.property("msgTo"));
criteria.setProjection(projection);

criteria.setResultTransformer(Transformers.aliasToBean(Message.class));
List<String> msgFromList = criteria.list();

As per your question first solution gives correct output.

Answer 3

In case You want to get a whole Entity with DISTINCT you can use Projections.Entity

Criteria.SetProjection(
Projections.Distinct(Projections.Entity(typeof(YourEntityHere), "this")));

"this" means root entity.

Answer 4

As @APC response

it works and it can be more clear as

SELECT FROM Object o 
WHERE o.propCondition = condition
GROUP BY o.propDistinct

Answer 5

Below is the sample query :

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

Alternatively, you can also use Criteria API.

Answer 6

I have got a answer for Hibernate Query Language to use Distinct fields. You can use SELECT DISTINCT(TO_CITY) FROM FLIGHT_ROUTE. If you use SQL query, it return String List. You can't use it return value by Entity Class. So the Answer to solve that type of Problem is use HQL with SQL.

"FROM FLIGHT_ROUTE F WHERE F.ROUTE_ID IN (SELECT SF.ROUTE_ID FROM FLIGHT_ROUTE SF GROUP BY SF.TO_CITY)";

From SQL query statement it got DISTINCT ROUTE_ID and input as a List. And IN query filter the distinct TO_CITY from IN (List).

Return type is Entity Bean type. So you can it in AJAX such as AutoComplement.

May all be OK