Preserve given Id on insert.

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-mongodb-parent</artifactId>
-	<version>4.0.0-SNAPSHOT</version>
+	<version>4.0.x-GH-4184-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>4.0.0-SNAPSHOT</version>
+		<version>4.0.x-GH-4184-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb-distribution/pom.xml

@@ -15,7 +15,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>4.0.0-SNAPSHOT</version>
+		<version>4.0.x-GH-4184-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb/pom.xml

@@ -13,7 +13,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>4.0.0-SNAPSHOT</version>
+		<version>4.0.x-GH-4184-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

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

@@ -1326,9 +1326,10 @@ default long exactCount(Query query, String collectionName) {
 	/**
 	 * Insert the object into the collection for the entity type of the object to save. <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. <br />
-	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
-	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
-	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See
+	 * If your object has an {@literal Id} property which holds a {@literal null} value, it will be set with the generated
+	 * Id from MongoDB. If your Id property is a String then MongoDB ObjectId will be used to populate that string.
+	 * Otherwise, the conversion from ObjectId to your property type will be handled by Spring's BeanWrapper class that
+	 * leverages Type Conversion API. See
 	 * <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation" > Spring's
 	 * Type Conversion"</a> for more details. <br />
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.

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

@@ -272,7 +272,7 @@ <T> MappedDocument prepareId(Class<T> type) {
 		 */
 		<T> MappedDocument prepareId(@Nullable MongoPersistentEntity<T> entity) {
 
-			if (entity == null) {
+			if (entity == null || source.hasId()) {
 				return source;
 			}
 

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

@@ -1093,9 +1093,10 @@ default Mono<Long> exactCount(Query query, String collectionName) {
 	/**
 	 * Insert the object into the collection for the entity type of the object to save. <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. <br />
-	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
-	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
-	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See
+	 * If your object has an {@literal Id} property which holds a {@literal null} value, it will be set with the generated
+	 * Id from MongoDB. If your Id property is a String then MongoDB ObjectId will be used to populate that string.
+	 * Otherwise, the conversion from ObjectId to your property type will be handled by Spring's BeanWrapper class that
+	 * leverages Type Conversion API. See
 	 * <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation" > Spring's
 	 * Type Conversion"</a> for more details. <br />
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.

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

@@ -3636,6 +3636,26 @@ public void saveAndLoadStringThatIsAnObjectIdAsString() {
 		assertThat(target).isEqualTo(source);
 	}
 
+	@Test // GH-4184
+	void insertHonorsExistingRawId() {
+
+		RawStringId source = new RawStringId();
+		source.id = "abc";
+		source.value = "new value";
+
+		template.insert(source);
+
+		org.bson.Document result = template
+				.execute(db -> db.getCollection(template.getCollectionName(RawStringId.class))
+						.find().limit(1).cursor().next());
+
+		assertThat(result).isNotNull();
+		assertThat(result.get("_id")).isEqualTo("abc");
+
+		RawStringId target = template.findOne(query(where("id").is(source.id)), RawStringId.class);
+		assertThat(target).isEqualTo(source);
+	}
+
 	@Test // GH-4026
 	void saveShouldGenerateNewIdOfTypeIfExplicitlyDefined() {
 

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

@@ -205,6 +205,15 @@ void insertContextDoesNotAddConvertedIdForMongoIdTypesTargetingObjectId() {
 				});
 	}
 
+	@Test // GH-4184
+	void insertContextDoesNotOverrideExistingId() {
+
+		assertThat(queryOperations.createInsertContext(new Document("_id", "abc")).prepareId(Person.class).getDocument())//
+				.satisfies(result -> {
+					assertThat(result).isEqualTo(new Document("_id", "abc"));
+				});
+	}
+
 	static class Person {
 
 	}

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

@@ -218,6 +218,23 @@ void insertShouldGenerateNewIdOfTypeIfExplicitlyDefined() {
 				}).verifyComplete();
 	}
 
+	@Test // GH-4184
+	void insertHonorsExistingRawId() {
+
+		MongoTemplateTests.RawStringId source = new MongoTemplateTests.RawStringId();
+		source.id = "abc";
+		source.value = "new value";
+
+		template.insert(source)
+				.then(template.execute(db -> Flux.from(
+						db.getCollection(template.getCollectionName(MongoTemplateTests.RawStringId.class)).find().limit(1).first()))
+						.next())
+				.as(StepVerifier::create).consumeNextWith(result -> {
+					assertThat(result).isNotNull();
+					assertThat(result.get("_id")).isEqualTo("abc");
+				});
+	}
+
 	@Test // DATAMONGO-1444
 	void insertsSimpleEntityCorrectly() {