[hibernate-dev] CriteriaBuilder, aggregation and types

[Guillaume Smet]

Test added to your PR. It passes now.

On Tue, Oct 16, 2018 at 10:02 AM Guillaume Smet <guillaume.smet at gmail.com>
wrote:

> Fabio put together a test in his PR:
> https://github.com/hibernate/hibernate-orm/pull/2568/files#diff-ab60fb95866b43def421ef53163885ccR1
>
> On Tue, Oct 16, 2018 at 4:38 AM Steve Ebersole <steve at hibernate.org>
> wrote:
>
>> Are there actual tests for this besides the full zip on the issue?  How
>> did you guys investigate this?
>>
>> On Mon, Oct 15, 2018 at 7:50 AM Guillaume Smet <guillaume.smet at gmail.com>
>> wrote:
>>
>>> OK, ping me when you're ready!
>>>
>>> On Mon, Oct 15, 2018 at 1:39 PM Steve Ebersole <steve at hibernate.org>
>>> wrote:
>>>
>>>> Let's discuss on Hip Chat in a few after I have woken up and had some
>>>> coffee :)
>>>>
>>>>
>>>> On Mon, Oct 15, 2018, 6:02 AM Guillaume Smet <guillaume.smet at gmail.com>
>>>> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> We discussed a bit more with Fabio on Friday and we ended up
>>>>> discovering
>>>>> that we have an issue with most Expressions that contain nested
>>>>> Expressions.
>>>>>
>>>>> The Renderable contract is defined with these 3 methods:
>>>>>     String render(RenderingContext renderingContext);
>>>>>
>>>>>     default String renderProjection(RenderingContext renderingContext)
>>>>> {
>>>>>         return render( renderingContext );
>>>>>     }
>>>>>
>>>>>     default String renderGroupBy(RenderingContext renderingContext) {
>>>>>         return render( renderingContext );
>>>>>     }
>>>>>
>>>>> The issue is that most of the Expressions containting nested
>>>>> Expressions
>>>>> only implement render().
>>>>>
>>>>> This means that you basically do the following:
>>>>> call renderProjection() -> expression1 only implement render() -> we
>>>>> call
>>>>> render() on the nested expressions instead of renderProjection().
>>>>>
>>>>> One possible workaround is to do what was done in
>>>>> SearchedCaseExpression
>>>>> for all the Expressions containing nested expressions (e.g. implement
>>>>> the 3
>>>>> methods and have a private method taking a lambda to propagate the
>>>>> variation).
>>>>>
>>>>> You can see an example of this change here:
>>>>>
>>>>> https://github.com/hibernate/hibernate-orm/pull/2568/files#diff-8fcc837a76b1af31f11e16a01332fd1dR96
>>>>> .
>>>>>
>>>>> Note that it has to be done for *all* the Expressions containing nested
>>>>> expressions. Either that or we simplify the Renderable contract to have
>>>>> only one render() method and a parameter defining the context. That
>>>>> would
>>>>> allow to avoid all these changes.
>>>>>
>>>>> Thoughts?
>>>>>
>>>>> --
>>>>> Guillaume
>>>>>
>>>>> On Thu, Oct 11, 2018 at 4:01 PM Guillaume Smet <
>>>>> guillaume.smet at gmail.com>
>>>>> wrote:
>>>>>
>>>>> > 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/main/java/org/hibernate/dialect/function/StandardAnsiSqlAggregationFunctions.java#L157
>>>>> >
>>>>> > 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/main/java/org/hibernate/query/criteria/internal/expression/ExpressionImpl.java#L35
>>>>> ).
>>>>> > 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
>>>>> >
>>>>> _______________________________________________
>>>>> hibernate-dev mailing list
>>>>> hibernate-dev at lists.jboss.org
>>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>>>>>
>>>>