The transform method throws a ClassCastException when working with joinFetch since 4.4.0

[miki1029]

Observed vs. expected behavior

The transform method throws a ClassCastException when working with joinFetch.

Steps to reproduce

I upload code here.
https://github.com/miki1029/querydsl-transform-bug

// no error
    @Transactional(readOnly = true)
    public Map<Long, Parent> getWithoutFetchJoin(Long id) {
        return from(parent)
                .leftJoin(parent.children)
                .where(parent.id.eq(id))
                .transform(groupBy(parent.id).as(parent));
    }

// error
    @Transactional(readOnly = true)
    public Map<Long, Parent> getWithFetchJoin(Long id) {
        return from(parent)
                .leftJoin(parent.children)
                .fetchJoin()
                .where(parent.id.eq(id))
                .distinct()
                .transform(groupBy(parent.id).as(parent));
    }

Environment

https://github.com/miki1029/querydsl-transform-bug/blob/master/build.gradle

Querydsl version: 5.0.0 (I got the same error in 4.4.0, not in 4.3.1.)

Querydsl module:

    implementation "com.querydsl:querydsl-jpa"
    annotationProcessor "jakarta.persistence:jakarta.persistence-api"
    annotationProcessor "jakarta.annotation:jakarta.annotation-api"
    annotationProcessor group: "com.querydsl", name: "querydsl-apt", classifier: "jpa"

Database: H2

JDK: openjdk11

Additional details

java.lang.IllegalStateException: Failed to execute CommandLineRunner
	at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:780) ~[spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:761) ~[spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:310) ~[spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312) ~[spring-boot-2.6.7.jar:2.6.7]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301) ~[spring-boot-2.6.7.jar:2.6.7]
	at com.example.querydsltransformbug.QuerydslTransformBugApplication.main(QuerydslTransformBugApplication.java:26) ~[main/:na]
Caused by: java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class com.querydsl.core.Tuple ([Ljava.lang.Object; is in module java.base of loader 'bootstrap'; com.querydsl.core.Tuple is in unnamed module of loader 'app')
	at com.querydsl.core.group.GroupByMap.transform(GroupByMap.java:57) ~[querydsl-core-5.0.0.jar:na]
	at com.querydsl.core.group.GroupByMap.transform(GroupByMap.java:35) ~[querydsl-core-5.0.0.jar:na]
	at com.querydsl.core.support.FetchableQueryBase.transform(FetchableQueryBase.java:55) ~[querydsl-core-5.0.0.jar:na]
	at com.example.querydsltransformbug.ParentService.getWithFetchJoin(ParentService.java:45) ~[main/:na]
	at com.example.querydsltransformbug.ParentService$$FastClassBySpringCGLIB$$a913a3eb.invoke(<generated>) ~[main/:na]
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) ~[spring-core-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:793) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:137) ~[spring-tx-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:123) ~[spring-tx-5.3.19.jar:5.3.19]
	at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:388) ~[spring-tx-5.3.19.jar:5.3.19]
	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:119) ~[spring-tx-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:708) ~[spring-aop-5.3.19.jar:5.3.19]
	at com.example.querydsltransformbug.ParentService$$EnhancerBySpringCGLIB$$82705e06.getWithFetchJoin(<generated>) ~[main/:na]
	at com.example.querydsltransformbug.QuerydslTransformBugApplication.run(QuerydslTransformBugApplication.java:36) ~[main/:na]
	at com.example.querydsltransformbug.QuerydslTransformBugApplication$$FastClassBySpringCGLIB$$123f3653.invoke(<generated>) ~[main/:na]
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) ~[spring-core-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:793) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:137) ~[spring-tx-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763) ~[spring-aop-5.3.19.jar:5.3.19]
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:708) ~[spring-aop-5.3.19.jar:5.3.19]
	at com.example.querydsltransformbug.QuerydslTransformBugApplication$$EnhancerBySpringCGLIB$$f479204c.run(<generated>) ~[main/:na]
	at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:777) ~[spring-boot-2.6.7.jar:2.6.7]
	... 5 common frames omitted

[jwgmeligmeyling]

You're only allowed to fetchJoin relations that are selected in the select clause.

Instead of throwing an exception Hibernate probably implicitly adds the children to the selection but this unfortunately means that the output from the query differs from what Querydsl expects.

Adding the child relation to your projection should fix the issue.

[svenrienstra]

I'm pretty sure this is actually a bug in Hibernate. The ResultTransformer to transform the result into a Tuple is not applied by Hibernate when FetchingScrollableResultsImpl is used. FetchingScrollableResultsImpl simply returns:

currentRow = new Object[] {row};

while ScrollableResultsImpl applies the ResultTransformer through the HolderInstantiator:

currentRow = new Object[] { getHolderInstantiator().instantiate( currentRow ) };

	public Object instantiate(Object[] row) {
		if (transformer==null) {
			return row;
		}
		else {
			return transformer.transformTuple(row, getQueryReturnAliases());
		}
	}

To work around this I've changed the AbstractGroupByTransformer implementations from:

 while (iter.hasNext()) {
                @SuppressWarnings("unchecked") //This type is mandated by the key type
                K[] row = (K[]) iter.next().toArray();

to

 while (iter.hasNext()) {
                Object next = iter.next();
                Tuple tuple;
                if (next instanceof Tuple) {
                    tuple = (Tuple) next;
                } else if (next instanceof Object[]) {
                    tuple = Projections.tuple(expressions).newInstance((Object[])next);
                } else {
                    throw new IllegalArgumentException(String.format("Could not translate %s into tuple", next));
                }

                K[] row = (K[]) tuple.toArray();

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[kamilkrzywanski]

@miki1029
created pr here: OpenFeign/querydsl#534