HHH-16740 Add a test case to reproduce the issue

hibernate-core/src/test/java/org/hibernate/orm/test/batch/CompositeIdAndElementCollectionBatchingTest.java

@@ -0,0 +1,128 @@
+package org.hibernate.orm.test.batch;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.Serializable;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.hibernate.cfg.Environment;
+
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.JiraKey;
+import org.hibernate.testing.orm.junit.ServiceRegistry;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+import org.hibernate.testing.orm.junit.Setting;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import jakarta.persistence.ElementCollection;
+import jakarta.persistence.Embeddable;
+import jakarta.persistence.EmbeddedId;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.MapsId;
+
+@DomainModel(
+		annotatedClasses = {
+				CompositeIdAndElementCollectionBatchingTest.EntityA.class,
+				CompositeIdAndElementCollectionBatchingTest.EntityB.class,
+				CompositeIdAndElementCollectionBatchingTest.EmbeddableA.class,
+				CompositeIdAndElementCollectionBatchingTest.EntityId.class
+		}
+)
+@SessionFactory
+@ServiceRegistry(
+		settings = @Setting(name = Environment.DEFAULT_BATCH_FETCH_SIZE, value = "2")
+)
+@JiraKey("HHH-16740")
+class CompositeIdAndElementCollectionBatchingTest {
+
+	private static final EntityB ENTITY_B = new EntityB( 1L );
+	private static final EntityA ENTITY_A = new EntityA(
+			new EntityId( "EntityA", ENTITY_B ),
+			Collections.singleton( new EmbeddableA( "EmbeddableA" ) )
+	);
+
+	@BeforeEach
+	public void setUp(SessionFactoryScope scope) {
+		scope.inTransaction(
+				entityManager -> {
+					entityManager.persist( ENTITY_B );
+					entityManager.persist( ENTITY_A );
+				}
+		);
+	}
+
+	@Test
+	void testSelect(SessionFactoryScope scope) {
+		scope.inTransaction(
+				entityManager -> {
+					EntityA a = entityManager.find( EntityA.class, ENTITY_A.id );
+					assertThat( a.elementCollection ).hasSize( 1 );
+				}
+		);
+	}
+
+	@Entity(name = "EntityA")
+	public static class EntityA {
+		@EmbeddedId
+		private EntityId id;
+
+		@ElementCollection
+		public Set<EmbeddableA> elementCollection = new HashSet<>();
+
+		public EntityA() {
+		}
+
+		public EntityA(EntityId id, Set<EmbeddableA> elementCollection) {
+			this.id = id;
+			this.elementCollection = elementCollection;
+		}
+	}
+
+	@Entity(name = "EntityB")
+	public static class EntityB {
+		@Id
+		private Long id;
+
+		public EntityB() {
+		}
+
+		public EntityB(Long id) {
+			this.id = id;
+		}
+	}
+
+	@Embeddable
+	public static class EntityId implements Serializable {
+		private String id1;
+		@ManyToOne
+		@MapsId
+		private EntityB id2;
+
+		public EntityId() {
+		}
+
+		public EntityId(String id1, EntityB id2) {
+			this.id1 = id1;
+			this.id2 = id2;
+		}
+	}
+
+	@Embeddable
+	public static class EmbeddableA {
+		private String name;
+
+		public EmbeddableA() {
+		}
+
+		public EmbeddableA(String name) {
+			this.name = name;
+		}
+	}
+
+}