HHH-19142 StatelessSession.getMultiple() and second-level cache

hibernate-core/src/main/java/org/hibernate/internal/StatelessSessionImpl.java

@@ -757,19 +757,45 @@ public <T> List<T> getMultiple(Class<T> entityClass, List<Object> ids) {
 				throw new IllegalArgumentException("Null id");
 			}
 		}
+
 		final EntityPersister persister = requireEntityPersister( entityClass.getName() );
+
+		final List<Object> uncachedIds;
+		final List<T> list = new ArrayList<>( ids.size() );
+		if ( persister.canReadFromCache() ) {
+			uncachedIds = new ArrayList<>( ids.size() );
+			for (Object id : ids) {
+				final Object cachedEntity =
+						loadFromSecondLevelCache( this, null, LockMode.NONE, persister,
+								generateEntityKey( id, persister ) );
+				if ( cachedEntity == null ) {
+					uncachedIds.add( id );
+					list.add( null );
+				}
+				else {
+					//noinspection unchecked
+					list.add( (T) cachedEntity );
+				}
+			}
+		}
+		else {
+			uncachedIds = ids;
+			for (int i = 0; i < ids.size(); i++) {
+				list.add( null );
+			}
+		}
+
 		final JpaCriteriaQuery<T> query = getCriteriaBuilder().createQuery(entityClass);
 		final JpaRoot<T> from = query.from(entityClass);
-		query.where( from.get( persister.getIdentifierPropertyName() ).in(ids) );
+		query.where( from.get( persister.getIdentifierPropertyName() ).in(uncachedIds) );
 		final List<T> resultList = createSelectionQuery(query).getResultList();
-		final List<Object> idList = new ArrayList<>( resultList.size() );
-		for (T entity : resultList) {
-			idList.add( persister.getIdentifier(entity, this) );
-		}
-		final List<T> list = new ArrayList<>( ids.size() );
-		for (Object id : ids) {
-			final int pos = idList.indexOf(id);
-			list.add( pos < 0 ? null : resultList.get(pos) );
+		for (int i = 0; i < ids.size(); i++) {
+			if ( list.get(i) == null ) {
+				final Object id = ids.get(i);
+				list.set( i, resultList.stream()
+						.filter( entity -> entity != null && persister.getIdentifier( entity, this ).equals(id) )
+						.findFirst().orElse( null ) );
+			}
 		}
 		return list;
 	}

hibernate-core/src/test/java/org/hibernate/orm/test/stateless/GetMultipleFromCacheTest.java

@@ -0,0 +1,57 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.orm.test.stateless;
+
+import jakarta.persistence.Cacheable;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+@SessionFactory(generateStatistics = true)
+@DomainModel(annotatedClasses = GetMultipleFromCacheTest.Record.class)
+public class GetMultipleFromCacheTest {
+	@Test void test(SessionFactoryScope scope) {
+		scope.inStatelessTransaction(s-> {
+			s.insert(new Record(123L,"hello earth"));
+			s.insert(new Record(456L,"hello mars"));
+		});
+		scope.inStatelessTransaction(s-> {
+			List<Record> all = s.getMultiple(Record.class, List.of(456L, 123L, 2L));
+			assertEquals("hello mars",all.get(0).message);
+			assertEquals("hello earth",all.get(1).message);
+			assertNull(all.get(2));
+		});
+		scope.getSessionFactory().getStatistics().clear();
+		scope.inStatelessTransaction(s-> {
+			List<Record> all = s.getMultiple(Record.class, List.of(123L, 2L, 456L));
+			assertEquals("hello earth",all.get(0).message);
+			assertEquals("hello mars",all.get(2).message);
+			assertNull(all.get(1));
+		});
+		assertEquals( 2,
+				scope.getSessionFactory().getStatistics().getSecondLevelCacheHitCount() );
+	}
+	@Entity @Cacheable
+	static class Record {
+		@Id Long id;
+		String message;
+
+		Record(Long id, String message) {
+			this.id = id;
+			this.message = message;
+		}
+
+		Record() {
+		}
+	}
+}

hibernate-core/src/test/java/org/hibernate/orm/test/stateless/GetMultipleTest.java

@@ -30,6 +30,12 @@ public class GetMultipleTest {
 			assertEquals("hello earth",all.get(1).message);
 			assertNull(all.get(2));
 		});
+		scope.inStatelessTransaction(s-> {
+			List<Record> all = s.getMultiple(Record.class, List.of(123L, 2L, 456L));
+			assertEquals("hello earth",all.get(0).message);
+			assertEquals("hello mars",all.get(2).message);
+			assertNull(all.get(1));
+		});
 	}
 	@Entity
 	static class Record {