Fix field projection value conversion.

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-mongodb-parent</artifactId>
-	<version>3.3.0-SNAPSHOT</version>
+	<version>3.3.0-GH-3668-SNAPSHOT</version>
 	<packaging>pom</packaging>
 
 	<name>Spring Data MongoDB</name>

spring-data-mongodb-benchmarks/pom.xml

@@ -7,7 +7,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.3.0-SNAPSHOT</version>
+		<version>3.3.0-GH-3668-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb-distribution/pom.xml

@@ -14,7 +14,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.3.0-SNAPSHOT</version>
+		<version>3.3.0-GH-3668-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb/pom.xml

@@ -11,7 +11,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.3.0-SNAPSHOT</version>
+		<version>3.3.0-GH-3668-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

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

@@ -195,19 +195,7 @@ public Document getMappedSort(Document sortObject, @Nullable MongoPersistentEnti
 			return new Document();
 		}
 
-		sortObject = filterUnwrappedObjects(sortObject, entity);
-
-		Document mappedSort = new Document();
-		for (Map.Entry<String, Object> entry : BsonUtils.asMap(sortObject).entrySet()) {
-
-			Field field = createPropertyField(entity, entry.getKey(), mappingContext);
-			if (field.getProperty() != null && field.getProperty().isUnwrapped()) {
-				continue;
-			}
-
-			mappedSort.put(field.getMappedKey(), entry.getValue());
-		}
-
+		Document mappedSort = mapFieldsToPropertyNames(sortObject, entity);
 		mapMetaAttributes(mappedSort, entity, MetaMapping.WHEN_PRESENT);
 		return mappedSort;
 	}
@@ -225,13 +213,30 @@ public Document getMappedFields(Document fieldsObject, @Nullable MongoPersistent
 
 		Assert.notNull(fieldsObject, "FieldsObject must not be null!");
 
-		fieldsObject = filterUnwrappedObjects(fieldsObject, entity);
-
-		Document mappedFields = getMappedObject(fieldsObject, entity);
+		Document mappedFields = mapFieldsToPropertyNames(fieldsObject, entity);
 		mapMetaAttributes(mappedFields, entity, MetaMapping.FORCE);
 		return mappedFields;
 	}
 
+	private Document mapFieldsToPropertyNames(Document fields, @Nullable MongoPersistentEntity<?> entity) {
+
+		if(fields.isEmpty()) {
+			return new Document();
+
+		}
+		Document target = new Document();
+		for (Map.Entry<String, Object> entry : BsonUtils.asMap(filterUnwrappedObjects(fields, entity)).entrySet()) {
+
+			Field field = createPropertyField(entity, entry.getKey(), mappingContext);
+			if (field.getProperty() != null && field.getProperty().isUnwrapped()) {
+				continue;
+			}
+
+			target.put(field.getMappedKey(), entry.getValue());
+		}
+		return target;
+	}
+
 	private void mapMetaAttributes(Document source, @Nullable MongoPersistentEntity<?> entity, MetaMapping metaMapping) {
 
 		if (entity == null) {

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

@@ -50,6 +50,7 @@
 import org.springframework.data.mongodb.core.mapping.Document;
 import org.springframework.data.mongodb.core.mapping.Field;
 import org.springframework.data.mongodb.core.mapping.FieldType;
+import org.springframework.data.mongodb.core.mapping.MongoId;
 import org.springframework.data.mongodb.core.mapping.MongoMappingContext;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.TextScore;
@@ -1304,6 +1305,13 @@ void allowsUsingFieldPathsForPropertiesHavingCustomConversionRegistered() {
 		assertThat(mapper.getMappedSort(query.getQueryObject(), context.getPersistentEntity(Customer.class))).isEqualTo(new org.bson.Document("address.street", "1007 Mountain Drive"));
 	}
 
+	@Test // GH-3668
+	void mapStringIdFieldProjection() {
+
+		org.bson.Document mappedFields = mapper.getMappedFields(new org.bson.Document("id", 1), context.getPersistentEntity(WithStringId.class));
+		assertThat(mappedFields).containsEntry("_id", 1);
+	}
+
 	class WithDeepArrayNesting {
 
 		List<WithNestedArray> level0;
@@ -1367,6 +1375,12 @@ class Sample {
 		@Id private String foo;
 	}
 
+	class WithStringId {
+
+		@MongoId String id;
+		String name;
+	}
+
 	class BigIntegerId {
 
 		@Id private BigInteger id;