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[#1644] Fix incorrect projection extraction for subqueries (use join … #2108

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[#1644] Fix incorrect projection extraction for subqueries (use join … #2108

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28 changes: 25 additions & 3 deletions ...essions/src/main/java/com/blazebit/persistence/querydsl/BlazeCriteriaBuilderRenderer.java
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,7 @@
import com.querydsl.core.types.ParamExpression;
import com.querydsl.core.types.Path;
import com.querydsl.core.types.Predicate;
import com.querydsl.core.types.Projections;
import com.querydsl.core.types.SubQueryExpression;
import com.querydsl.core.types.TemplateExpression;
import com.querydsl.core.types.Visitor;
Expand Down Expand Up @@ -260,14 +261,14 @@ public Object visit(SubQueryExpression<?> subQuery, Object criteriaBuilder) {
renderGroupBy(subQueryMetadata, (GroupByBuilder<?>) criteriaBuilder);
renderHaving(subQueryMetadata, (HavingBuilder<?>) criteriaBuilder);

Expression<?> select = subQueryMetadata.getProjection();
Expression<?> select = extractExpression(subQueryMetadata);
if (select instanceof FactoryExpression<?> && criteriaBuilder instanceof FullQueryBuilder<?, ?>) {
FactoryExpression<T> factoryExpression = (FactoryExpression<T>) select;
FullQueryBuilder<?, ?> fullQueryBuilder = (FullQueryBuilder<?, ?>) criteriaBuilder;
criteriaBuilder = fullQueryBuilder.selectNew(new FactoryExpressionObjectBuilder(factoryExpression));

} else {
List<? extends Expression<?>> projection = expandProjection(subQueryMetadata.getProjection());
List<? extends Expression<?>> projection = expandProjection(extractExpression(subQueryMetadata));

if (criteriaBuilder instanceof SelectBaseCTECriteriaBuilder) {
SelectBaseCTECriteriaBuilder<?> selectBaseCriteriaBuilder = (SelectBaseCTECriteriaBuilder<?>) criteriaBuilder;
Expand Down Expand Up @@ -905,6 +906,27 @@ private static String relativePathString(Path<?> root, Path<?> path) {
return pathString.toString();
}

private static Expression<?> extractExpression(QueryMetadata meta) {
Expression<?> projection = meta.getProjection();
if (projection != null) {
return projection;
}

List<JoinExpression> joins = meta.getJoins();
if (joins == null || joins.isEmpty()) {
return null;
}

JoinExpression firstJoin = joins.get(0);
if (firstJoin == null) {
return null;
}

return firstJoin.getType() == com.querydsl.core.JoinType.DEFAULT
? Projections.constructor(firstJoin.getTarget().getType())
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@jwgmeligmeyling jwgmeligmeyling Mar 15, 2026

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Is this a convenience (desugar) or query language feature? The PR is suggested as a fix but what states that subqueries without a projection were ever allowed in JPQL/JPQL Next?

Doing this kind of expression manipulation makes a few assumptions that may not always be true:

  • The entity is a class
  • The entity name is the classname
  • The entity name is the alias for the select expression

Please add a test case to https://github.com/Blazebit/blaze-persistence/blob/main/integration/querydsl/testsuite/src/test/java/com/blazebit/persistence/querydsl/BasicQueryTest.java so we can have a look that the desired query behaviour.

: null;
}

/**
* Visitor that parses {@link JPQLNextOps#WITH_ALIAS}.
*/
Expand Down Expand Up @@ -1523,7 +1545,7 @@ public Object visit(SubQueryExpression<?> expr, Object context) {

renderCTEs(metadata);

metadata.getProjection().accept(this, context);
extractExpression(metadata).accept(this, context);

for (QueryFlag flag : metadata.getFlags()) {
flag.getFlag().accept(this, context);
Expand Down