DATAMONGO-1361 - Guard command result statistics evaluation against changes in MongoDB 3.2.

MongoDB 3.2 RC1 decided to remove fields from statistics JSON documents returned in case no result was found for a geo near query. The avgDistance field is unfortunately missing as of that version.

Introduced a value object to encapsulate the mitigation behavior and make client code unaware of that.

Author: odrotbohm

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/GeoCommandStatistics.java

@@ -0,0 +1,72 @@
+/*
+ * 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.data.mongodb.core;
+
+import org.springframework.util.Assert;
+
+import com.mongodb.BasicDBObject;
+import com.mongodb.DBObject;
+
+/**
+ * Value object to mitigate different representations of geo command execution results in MongoDB.
+ * 
+ * @author Oliver Gierke
+ * @soundtrack Fruitcake - Jeff Coffin (The Inside of the Outside)
+ */
+class GeoCommandStatistics {
+
+	private static final GeoCommandStatistics NONE = new GeoCommandStatistics(new BasicDBObject());
+
+	private final DBObject source;
+
+	/**
+	 * Creates a new {@link GeoCommandStatistics} instance with the given source document.
+	 * 
+	 * @param source must not be {@literal null}.
+	 */
+	private GeoCommandStatistics(DBObject source) {
+
+		Assert.notNull(source, "Source document must not be null!");
+		this.source = source;
+	}
+
+	/**
+	 * Creates a new {@link GeoCommandStatistics} from the given command result extracting the statistics.
+	 * 
+	 * @param commandResult must not be {@literal null}.
+	 * @return
+	 */
+	public static GeoCommandStatistics from(DBObject commandResult) {
+
+		Assert.notNull(commandResult, "Command result must not be null!");
+
+		Object stats = commandResult.get("stats");
+		return stats == null ? NONE : new GeoCommandStatistics((DBObject) stats);
+	}
+
+	/**
+	 * Returns the average distance reported by the command result. Mitigating a removal of the field in case the command
+	 * didn't return any result introduced in MongoDB 3.2 RC1.
+	 * 
+	 * @return
+	 * @see https://jira.mongodb.org/browse/SERVER-21024
+	 */
+	public double getAverageDistance() {
+
+		Object averageDistance = source.get("avgDistance");
+		return averageDistance == null ? Double.NaN : (Double) averageDistance;
+	}
+}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java

@@ -694,9 +694,8 @@ public <T> GeoResults<T> geoNear(NearQuery near, Class<T> entityClass, String co
 			return new GeoResults<T>(result, near.getMetric());
 		}
 
-		DBObject stats = (DBObject) commandResult.get("stats");
-		double averageDistance = stats == null ? 0 : (Double) stats.get("avgDistance");
-		return new GeoResults<T>(result, new Distance(averageDistance, near.getMetric()));
+		GeoCommandStatistics stats = GeoCommandStatistics.from(commandResult);
+		return new GeoResults<T>(result, new Distance(stats.getAverageDistance(), near.getMetric()));
 	}
 
 	public <T> T findAndModify(Query query, Update update, Class<T> entityClass) {

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/GeoCommandStatisticsUnitTests.java

@@ -0,0 +1,65 @@
+/*
+ * 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.data.mongodb.core;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+import com.mongodb.BasicDBObject;
+
+/**
+ * Unit tests for {@link GeoCommandStatistics}.
+ * 
+ * @author Oliver Gierke
+ * @soundtrack Fruitcake - Jeff Coffin (The Inside of the Outside)
+ */
+public class GeoCommandStatisticsUnitTests {
+
+	/**
+	 * @see DATAMONGO-1361
+	 */
+	@Test(expected = IllegalArgumentException.class)
+	public void rejectsNullCommandResult() {
+		GeoCommandStatistics.from(null);
+	}
+
+	/**
+	 * @see DATAMONGO-1361
+	 */
+	@Test
+	public void fallsBackToNanIfNoAverageDistanceIsAvailable() {
+
+		GeoCommandStatistics statistics = GeoCommandStatistics.from(new BasicDBObject("stats", null));
+		assertThat(statistics.getAverageDistance(), is(Double.NaN));
+
+		statistics = GeoCommandStatistics.from(new BasicDBObject("stats", new BasicDBObject()));
+		assertThat(statistics.getAverageDistance(), is(Double.NaN));
+	}
+
+	/**
+	 * @see DATAMONGO-1361
+	 */
+	@Test
+	public void returnsAverageDistanceIfPresent() {
+
+		GeoCommandStatistics statistics = GeoCommandStatistics
+				.from(new BasicDBObject("stats", new BasicDBObject("avgDistance", 1.5)));
+
+		assertThat(statistics.getAverageDistance(), is(1.5));
+	}
+}