DATACASS-287 - Call QueryForObjectListener for absent singular responses.

QueryForObjectListener is now called passing null for absent responses when querying for one single object.

spring-cql/src/main/java/org/springframework/cassandra/core/QueryForObjectListener.java

@@ -1,22 +1,42 @@
+/*
+ * Copyright 2016 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
+ *
+ *      http://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.cassandra.core;
 
 import com.datastax.driver.core.ResultSet;
 
 /**
- * Listener used to receive asynchronous results expected as an object of type <code>T</code>.
+ * Listener used to receive asynchronous results expected as an object of type <code>T</code> or an {@link Exception}.
  * 
  * @author Matthew T. Adams
+ * @author Mark Paluch
  * @param <T>
  */
 public interface QueryForObjectListener<T> {
 
 	/**
 	 * Called upon query completion.
+	 * 
+	 * @param result the result, can be {@literal null} for empty single-record results.
 	 */
 	void onQueryComplete(T result);
 
 	/**
 	 * Called if an exception is raised while getting or converting the {@link ResultSet}.
+	 * 
+	 * @param ex the exception that triggered the failure, never {@link null}.
 	 */
-	void onException(Exception x);
+	void onException(Exception ex);
 }

spring-cql/src/test/java/org/springframework/cassandra/test/integration/core/async/ObjectListener.java

@@ -22,19 +22,21 @@ import org.springframework.cassandra.support.TestListener;
  * @author Matthew T. Adams
  * @author David Webb
  */
-class ObjectListener<T> extends TestListener implements QueryForObjectListener<T> {
+public class ObjectListener<T> extends TestListener implements QueryForObjectListener<T> {
 
-	T result;
-	Exception exception;
+	public volatile T result;
+	public volatile Exception exception;
 
 	@Override
 	public void onQueryComplete(T result) {
+
 		this.result = result;
 		countDown();
 	}
 
 	@Override
 	public void onException(Exception x) {
+
 		this.exception = x;
 		countDown();
 	}

spring-data-cassandra/src/main/java/org/springframework/data/cassandra/core/CassandraTemplate.java

@@ -1068,6 +1068,9 @@ public class CassandraTemplate extends CqlTemplate implements CassandraOperation
 						}
 						listener.onQueryComplete(result);
 					}
+					else{
+						listener.onQueryComplete(null);
+					}
 				} catch (Exception e) {
 					listener.onException(translateExceptionIfPossible(e));
 				}

spring-data-cassandra/src/test/java/org/springframework/data/cassandra/test/integration/core/AsynchronousCassandraTemplateIntegrationTests.java

@@ -15,6 +15,7 @@
  */
 package org.springframework.data.cassandra.test.integration.core;
 
+import static org.hamcrest.Matchers.*;
 import static org.junit.Assert.*;
 import static org.junit.Assume.*;
 import static org.springframework.data.cassandra.repository.support.BasicMapId.*;
@@ -34,6 +35,7 @@ import org.springframework.cassandra.core.PrimaryKeyType;
 import org.springframework.cassandra.core.RetryPolicy;
 import org.springframework.cassandra.core.WriteOptions;
 import org.springframework.cassandra.support.exception.CassandraConnectionFailureException;
+import org.springframework.cassandra.test.integration.core.async.ObjectListener;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.data.cassandra.core.CassandraOperations;
 import org.springframework.data.cassandra.core.CassandraTemplate;
@@ -199,6 +201,40 @@ public class AsynchronousCassandraTemplateIntegrationTests extends AbstractSprin
 		fail("should've thrown CancellationException");
 	}
 
+	/**
+	 * @see DATACASS-287
+	 */
+	@Test(timeout = 10000)
+	public void shouldSelectOneAsynchronously() throws Exception {
+
+		Thing thing = Thing.random();
+		cassandraOperations.insert(thing);
+
+		ObjectListener<Thing> objectListener = new ObjectListener<Thing>();
+		String cql = String.format("SELECT * from thing where stuff = '%s'", thing.stuff);
+
+		cassandraOperations.selectOneAsynchronously(cql, Thing.class, objectListener);
+		objectListener.await();
+
+		assertThat(objectListener.result, is(notNullValue()));
+		assertThat(objectListener.result.stuff, is(equalTo(thing.stuff)));
+	}
+
+	/**
+	 * @see DATACASS-287
+	 */
+	@Test(timeout = 10000)
+	public void shouldSelectOneAsynchronouslyIfObjectIsAbsent() throws Exception {
+
+		ObjectListener<Thing> objectListener = new ObjectListener<Thing>();
+		String cql = String.format("SELECT * from thing where stuff = '%s'", UUID.randomUUID());
+
+		cassandraOperations.selectOneAsynchronously(cql, Thing.class, objectListener);
+		objectListener.await();
+
+		assertThat(objectListener.result, is(nullValue()));
+	}
+
 	@Configuration
 	public static class Config extends IntegrationTestConfig {}