[hibernate-dev] CriteriaBuilder, aggregation and types

Hi, We have an interesting test case here https://hibernate.atlassian.net/browse/HHH-13001 about the use of LiteralHandlingMode with the criteria builder. It turns out that the problem is a bit more general than that. Let's take this (not so useful) example: query.multiselect( document.get( "id" ), cb.sum( cb.parameter( Long.class ) ) ) .groupBy( document.get( "id" ) ); It will lead to a NPE when trying to determine the return type of the sum in: https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src... The fact is that we totally lose the type information along the way. I don't know if it's something addressed in 6 and if we should try to fix it in 5.4. In any case, I think having a workaround would be nice. There are a few paths we could follow: 1/ at least throw a more meaningful error and provide a workaround. I thought about forcing the use of the cast function but it doesn't work as we have an optimization not adding the cast function is the type is corresponding (see https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src...). If we remove this one and provide a helpful error message, that could help. Note that I don't know if it's just an optimization or something mandated by the spec itself. 2/ we could try to add a cast automatically for these functions needing a proper type only when strictly necessary e.g. when you have a parameter (or a LiteralExpression transformed to a parameter). That would mean adding a method ExpressionImplementor (and change all our code to use ExpressionImplementor as it currently uses the JPA version mostly everywhere). That would be more transparent for the user but clearly a significant amount of (dumb) work/changes. And probably a nightmare to merge in 6 if this area has changed. Thoughts? -- Guillaume