Ignore fields with Optional.empty when performing Query by Example.

The Auditable interface introduces Optional getters, which when combined with Query by Example result in cryptic errors. By ignoring a probe's field that contains an Optional.empty, Query by Example works properly.

Closes #2176.

Author: gregturn

src/main/java/org/springframework/data/jpa/convert/QueryByExamplePredicateBuilder.java

@@ -56,6 +56,7 @@
  * @author Mark Paluch
  * @author Oliver Gierke
  * @author Jens Schauder
+ * @author Greg Turnquist
  * @since 1.10
  */
 public class QueryByExamplePredicateBuilder {
@@ -146,6 +147,10 @@ static List<Predicate> getPredicates(String path, CriteriaBuilder cb, Path<?> fr
 
 			Object attributeValue = optionalValue.get();
 
+			if (attributeValue == Optional.empty()) {
+				continue;
+			}
+
 			if (attribute.getPersistentAttributeType().equals(PersistentAttributeType.EMBEDDED)
 					|| (isAssociation(attribute) && !(from instanceof From))) {
 

src/test/java/org/springframework/data/jpa/domain/support/AuditableQueryByExampleTests.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2008-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.jpa.domain.support;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.util.List;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.data.domain.Example;
+import org.springframework.data.jpa.domain.sample.AuditableUser;
+import org.springframework.data.jpa.domain.sample.AuditorAwareStub;
+import org.springframework.data.jpa.repository.sample.AnnotatedAuditableUserRepository;
+import org.springframework.data.jpa.repository.sample.AuditableUserRepository;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+/**
+ * Integration test for {@link org.springframework.data.repository.query.QueryByExampleExecutor} involving
+ * {@link java.util.Optional}, using {@link org.springframework.data.domain.Auditable} as the means to verify it works
+ * properly.
+ *
+ * @author Greg Turnquist
+ */
+@ExtendWith(SpringExtension.class)
+@ContextConfiguration("classpath:auditing/auditing-query-by-example.xml")
+public class AuditableQueryByExampleTests {
+
+	@Autowired AuditableUserRepository repository;
+	@Autowired AnnotatedAuditableUserRepository annotatedUserRepository;
+
+	@Autowired AuditorAwareStub auditorAware;
+
+	private AuditableUser user;
+
+	@BeforeEach
+	void setUp() {
+
+		user = new AuditableUser();
+		auditorAware.setAuditor(user);
+
+		repository.saveAndFlush(user);
+	}
+
+	@Test
+	void queryByExampleTreatsEmptyOptionalsLikeNulls() {
+
+		user.setFirstname("Greg");
+		user = repository.saveAndFlush(user);
+
+		AuditableUser probe = new AuditableUser();
+		probe.setFirstname("Greg");
+		Example<AuditableUser> example = Example.of(probe);
+
+		List<AuditableUser> results = repository.findAll(example);
+
+		assertThat(results).hasSize(1);
+		assertThat(results).extracting(AuditableUser::getFirstname).containsExactly("Greg");
+	}
+}

src/test/resources/auditing/auditing-query-by-example.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns:jpa="http://www.springframework.org/schema/data/jpa"
+       xmlns:context="http://www.springframework.org/schema/context"
+       xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
+		http://www.springframework.org/schema/data/jpa https://www.springframework.org/schema/data/jpa/spring-jpa.xsd
+		http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
+
+    <import resource="../infrastructure.xml" />
+
+    <jpa:auditing auditor-aware-ref="auditorAware" />
+
+    <bean id="auditorAware" class="org.springframework.data.jpa.domain.sample.AuditorAwareStub">
+        <constructor-arg ref="auditableUserRepository" />
+    </bean>
+
+    <jpa:repositories base-package="org.springframework.data.jpa.repository.sample" />
+
+</beans>