DATAMONGO-1685 - Adapt to QueryByExampleExecutor API changes.

Use Optional as return type for findOne(Example example).

Related ticket: DATACMNS-1058.

Original pull request: spring-projects#460.

Author: christophstrobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/SimpleMongoRepository.java

@@ -312,12 +312,13 @@ public <S extends T> List<S> findAll(Example<S> example) {
 	 * @see org.springframework.data.repository.query.QueryByExampleExecutor#findOne(org.springframework.data.domain.Example)
 	 */
 	@Override
-	public <S extends T> S findOne(Example<S> example) {
+	public <S extends T> Optional<S> findOne(Example<S> example) {
 
 		Assert.notNull(example, "Sample must not be null!");
 
 		Query q = new Query(new Criteria().alike(example));
-		return mongoOperations.findOne(q, example.getProbeType(), entityInformation.getCollectionName());
+		return Optional
+				.ofNullable(mongoOperations.findOne(q, example.getProbeType(), entityInformation.getCollectionName()));
 	}
 
 	/*

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/ContactRepositoryIntegrationTests.java

@@ -31,6 +31,7 @@
  * 
  * @author Oliver Gierke
  * @author Mark Paluch
+ * @author Christoph Strobl
  */
 @RunWith(SpringJUnit4ClassRunner.class)
 @ContextConfiguration("config/MongoNamespaceIntegrationTests-context.xml")
@@ -57,6 +58,6 @@ public void findsContactByTypedExample() {
 
 		Person person = repository.save(new Person("Oliver", "Gierke"));
 
-		assertThat(repository.findOne(Example.of(person)), instanceOf(Person.class));
+		assertThat(repository.findOne(Example.of(person)).get(), instanceOf(Person.class));
 	}
 }

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/support/SimpleMongoRepositoryTests.java

@@ -29,6 +29,7 @@
 import java.util.Set;
 import java.util.UUID;
 
+import org.assertj.core.api.Assertions;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -376,9 +377,9 @@ public void findOneByExampleShouldLookUpEntriesCorrectly() {
 		sample.setLastname("Matthews");
 		trimDomainType(sample, "id", "createdAt", "email");
 
-		Person result = repository.findOne(Example.of(sample));
+		Optional<Person> result = repository.findOne(Example.of(sample));
 
-		assertThat(result, is(equalTo(dave)));
+		Assertions.assertThat(result).isPresent().contains(dave);
 	}
 
 	@Test // DATAMONGO-1245