Projections.countDistinct with Hibernate produces unexpected result

问题

I have the following code

Criteria criteria = this.getCriteriaForClass(DeviceListItem.class);
Projection rowCountProjection = Projections.countDistinct("color");
criteria.setProjection(rowCountProjection);
int rowCount = ((Long) criteria.uniqueResult()).intValue();
return rowCount;

, whose purpose is to find out the number of rows with different values for the field named "color". The problem is that

Projections.countDistinct("color");

returns the same number of results as

Projections.count("color");

even though there are multiple rows with same color in the database view. When converting the Criteria object to SQL, I see that the SQL produced by Hibernate is

select count(this_.COLOR) as y0_ from DEVICESLIST_VIEW this_ where 1=1

when I would expect it to be

select count(distinct this_.COLOR) as y0_ from DEVICESLIST_VIEW this_ where 1=1

Why doesn't it work like expected and is there some remedy? Unfortunately I have no option to use HQL in this case.

回答1:

It's a bug, fixed in 3.5.2: HHH-4957.

来源：https://stackoverflow.com/questions/4616607/projections-countdistinct-with-hibernate-produces-unexpected-result