DATAMONGO-1486 - Fix ClassCastException when mapping non-String Map key for updates.

We now make sure to convert Map keys into Strings when mapping update values for Map properties.

Original pull request: #387.

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

@@ -1012,7 +1012,8 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 				TypeInformation<? extends Object> valueTypeHint = typeHint != null && typeHint.getMapValueType() != null
 						? typeHint.getMapValueType() : typeHint;
 
-				converted.put(convertToMongoType(entry.getKey()), convertToMongoType(entry.getValue(), valueTypeHint));
+				converted.put(getPotentiallyConvertedSimpleWrite(entry.getKey()).toString(),
+						convertToMongoType(entry.getValue(), valueTypeHint));
 			}
 
 			return new BasicDBObject(converted);

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

@@ -914,6 +914,24 @@ public class UpdateMapperUnitTests {
 		assertThat(result, isBsonObject().containing("$set.enumAsMapKey.V", 100));
 	}
 
+	/**
+	 * @see DATAMONGO-1486
+	 */
+	@Test
+	public void mappingShouldConvertMapKeysToString() {
+
+		Update update = new Update().set("map", Collections.singletonMap(25, "#StarTrek50"));
+		DBObject mappedUpdate = mapper.getMappedObject(update.getUpdateObject(),
+				context.getPersistentEntity(EntityWithObjectMap.class));
+
+		DBObject $set = getAsDBObject(mappedUpdate, "$set");
+		DBObject mapToSet = getAsDBObject($set, "map");
+
+		for (Object key : mapToSet.keySet()) {
+			assertThat(key, instanceOf(String.class));
+		}
+	}
+
 	static class DomainTypeWrappingConcreteyTypeHavingListOfInterfaceTypeAttributes {
 		ListModelWrapper concreteTypeWithListAttributeOfInterfaceType;
 	}