Support Optional<> for Filters

So far, `Optional<>` was only supported on `findOne` methods.
Based on https://jira.spring.io/browse/DATACMNS-483 this change now also
support `Optional<>` for `findBy` methods.

Fixes #27.

Author: derjust

src/main/java/org/socialsignin/spring/data/dynamodb/query/AbstractMultipleEntityQuery.java

@@ -18,7 +18,6 @@
 import java.util.List;
 
 import org.socialsignin.spring.data.dynamodb.core.DynamoDBOperations;
-import org.springframework.dao.EmptyResultDataAccessException;
 import org.springframework.dao.IncorrectResultSizeDataAccessException;
 
 /**
@@ -38,8 +37,11 @@ public T getSingleResult() {
 			throw new IncorrectResultSizeDataAccessException("result returns more than one elements", 1, results.size());
 		}
 		if (results.size() == 0) {
-			throw new EmptyResultDataAccessException("No results found", 1);
+		// return null here as Spring will convert that to Optional if nessassary
+		// https://jira.spring.io/browse/DATACMNS-483
+			return null;
+		} else {
+			return results.get(0);
 		}
-		return results.get(0);
 	}
 }

src/test/java/org/socialsignin/spring/data/dynamodb/domain/sample/Jdk8IT.java

@@ -35,9 +35,9 @@ public static class TestAppConfig {
 	UserRepository userRepository;
 
 	@Test
-	public void testOptional() {
+	public void testOptionalKey() {
 		final Date joinDate = new Date(1000);
-		final String id = "testOptional";
+		final String id = "testOptionalKey";
 		Optional<User> result = userRepository.findOne(id);
 
 		assertNotNull(result);
@@ -55,6 +55,29 @@ public void testOptional() {
 		assertEquals(savedEntity, result.get());
 		assertEquals(joinDate, result.get().getJoinDate());
 	}
+	
+	@Test
+	public void testOptionalFilter() {
+        final Date joinDate = new Date(2000);
+        final String id = "testOptionalFilter";
+        final String name = UUID.randomUUID().toString();
+        Optional<User> result = userRepository.findByName(name);
+
+        assertNotNull(result);
+        assertEquals(result, Optional.empty());
+
+        User newUser = new User();
+        newUser.setId(id);
+        newUser.setName(name);
+        newUser.setJoinDate(joinDate);
+
+        User savedEntity = userRepository.save(newUser);
+
+        result = userRepository.findByName(name);
+        assertNotNull(result);
+        assertEquals(savedEntity, result.get());
+        assertEquals(joinDate, result.get().getJoinDate());
+	}
 
 	@Test
 	public void testInstantQuery() {

src/test/java/org/socialsignin/spring/data/dynamodb/domain/sample/UserRepository.java

@@ -15,5 +15,8 @@ public interface UserRepository extends Repository<User, String> {
 	@EnableScan
 	List<User> findByLeaveDate(Instant leaveDate);
 
+	@EnableScan
+	Optional<User> findByName(String name);
+
 	<T extends User> User save(T entity);
 }