Consider GROUP BY count queries in AOT repository fragments.

We now properly consider results of GROUP BY count queries returning potentially multiple rows, a count for each group instead of enforcing a single result item.

Closes #4096

Author: mp911de

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/aot/AotRepositoryFragmentSupport.java

@@ -15,12 +15,14 @@
  */
 package org.springframework.data.jpa.repository.aot;
 
+import jakarta.persistence.Query;
 import jakarta.persistence.Tuple;
 
 import java.lang.reflect.Array;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.List;
 import java.util.Optional;
 import java.util.function.UnaryOperator;
 import java.util.stream.Stream;
@@ -167,6 +169,24 @@ protected String rewriteQuery(DeclaredQuery query, Sort sort, Class<?> returnedT
 		return source;
 	}
 
+	protected long getCount(Query query) {
+
+		List<?> totals = query.getResultList();
+
+		if (totals.size() == 1) {
+			Object result = totals.get(0);
+
+			if (result instanceof Number n) {
+				return n.longValue();
+			}
+
+			return CONVERSION_SERVICE.convert(result, Long.class);
+		}
+
+		// group by count
+		return totals.size();
+	}
+
 	protected <T> @Nullable T convertOne(@Nullable Object result, boolean nativeQuery, Class<T> projection) {
 
 		if (result == null) {

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/aot/JpaCodeBlocks.java

@@ -226,7 +226,7 @@ public CodeBlock build() {
 				builder.add(createQuery(true, countQueryVariableName, countQueryStringNameVariableName, queryRewriterName,
 						queries.count(), null, pageable,
 						queryHints ? this.queryHints : MergedAnnotation.missing(), null, Long.class));
-				builder.addStatement("return ($T) $L.getSingleResult()", Long.class, countQueryVariableName);
+				builder.addStatement("return getCount($L)", countQueryVariableName);
 
 				// end control flow does not work well with lambdas
 				builder.unindent();

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/UserRepositoryTests.java

@@ -418,7 +418,7 @@ void testPreventsCascadingRolePersisting() {
 	 * Tests cascading on {@literal merge} operation.
 	 */
 	@Test
-	void testMergingCascadesCollegueas() {
+	void testMergingCascadesColleagues() {
 
 		firstUser.addColleague(secondUser);
 		flushTestUsers();
@@ -752,13 +752,18 @@ void findsUsersBySpringDataNamedQuery() {
 		assertThat(repository.findBySpringDataNamedQuery("Gierke")).containsOnly(firstUser);
 	}
 
-	@Test // DATADOC-86
+	@Test // DATADOC-86, GH-4096
 	void readsPageWithGroupByClauseCorrectly() {
 
 		flushTestUsers();
 
+		repository.saveAndFlush(new User("Foo", "raymond", "[email protected]"));
+
 		Page<String> result = repository.findByLastnameGrouped(PageRequest.of(0, 10));
 		assertThat(result.getTotalPages()).isOne();
+
+		assertThat(repository.findByLastnameGrouped(PageRequest.of(0, 3))).hasSize(3);
+		assertThat(repository.findByLastnameGrouped(PageRequest.of(1, 2))).hasSize(2);
 	}
 
 	@Test