Generate and convert id on insert if explicitly defined.

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-mongodb-parent</artifactId>
-	<version>4.0.0-SNAPSHOT</version>
+	<version>4.0.0-GH-4026-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>4.0.0-GH-4026-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>4.0.0-GH-4026-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb/pom.xml

@@ -12,7 +12,7 @@
   <parent>
     <groupId>org.springframework.data</groupId>
     <artifactId>spring-data-mongodb-parent</artifactId>
-    <version>4.0.0-SNAPSHOT</version>
+    <version>4.0.0-GH-4026-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 

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

@@ -97,6 +97,16 @@ public Document getDocument() {
 		return this.document;
 	}
 
+	/**
+	 * Updates the documents {@link #ID_FIELD}.
+	 *
+	 * @param value the {@literal _id} value to set.
+	 * @since 3.4.1
+	 */
+	public void updateId(Object value) {
+		document.put(ID_FIELD, value);
+	}
+
 	/**
 	 * An {@link UpdateDefinition} that indicates that the {@link #getUpdateObject() update object} has already been
 	 * mapped to the specific domain type.

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

@@ -30,6 +30,7 @@
 import org.apache.commons.logging.LogFactory;
 import org.bson.Document;
 import org.bson.conversions.Bson;
+import org.bson.types.ObjectId;
 import org.springframework.beans.BeansException;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
@@ -83,6 +84,7 @@
 import org.springframework.data.mongodb.core.index.IndexOperationsProvider;
 import org.springframework.data.mongodb.core.index.MongoMappingEventPublisher;
 import org.springframework.data.mongodb.core.index.MongoPersistentEntityIndexCreator;
+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.MongoPersistentProperty;
@@ -1392,18 +1394,20 @@ protected Object insertDocument(String collectionName, Document document, Class<
 					collectionName));
 		}
 
+		MappedDocument mappedDocument = queryOperations.createInsertContext(MappedDocument.of(document)).prepareId(entityClass);
+
 		return execute(collectionName, collection -> {
 			MongoAction mongoAction = new MongoAction(writeConcern, MongoActionOperation.INSERT, collectionName, entityClass,
-					document, null);
+					mappedDocument.getDocument(), null);
 			WriteConcern writeConcernToUse = prepareWriteConcern(mongoAction);
 
 			if (writeConcernToUse == null) {
-				collection.insertOne(document);
+				collection.insertOne(mappedDocument.getDocument());
 			} else {
-				collection.withWriteConcern(writeConcernToUse).insertOne(document);
+				collection.withWriteConcern(writeConcernToUse).insertOne(mappedDocument.getDocument());
 			}
 
-			return operations.forEntity(document).getId();
+			return operations.forEntity(mappedDocument.getDocument()).getId();
 		});
 	}
 
@@ -1454,7 +1458,9 @@ protected Object saveDocument(String collectionName, Document dbDoc, Class<?> en
 					: collection.withWriteConcern(writeConcernToUse);
 
 			if (!mapped.hasId()) {
-				collectionToUse.insertOne(dbDoc);
+
+				mapped = queryOperations.createInsertContext(mapped).prepareId(mappingContext.getPersistentEntity(entityClass));
+				collectionToUse.insertOne(mapped.getDocument());
 			} else {
 
 				MongoPersistentEntity<?> entity = mappingContext.getPersistentEntity(entityClass);

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

@@ -28,7 +28,7 @@
 import org.bson.BsonValue;
 import org.bson.Document;
 import org.bson.codecs.Codec;
-
+import org.bson.types.ObjectId;
 import org.springframework.data.mapping.PropertyPath;
 import org.springframework.data.mapping.PropertyReferenceException;
 import org.springframework.data.mapping.context.MappingContext;
@@ -46,6 +46,7 @@
 import org.springframework.data.mongodb.core.aggregation.TypedAggregation;
 import org.springframework.data.mongodb.core.convert.QueryMapper;
 import org.springframework.data.mongodb.core.convert.UpdateMapper;
+import org.springframework.data.mongodb.core.mapping.MongoId;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
 import org.springframework.data.mongodb.core.mapping.ShardKey;
@@ -107,6 +108,14 @@ class QueryOperations {
 		this.aggregationUtil = new AggregationUtil(queryMapper, mappingContext);
 	}
 
+	InsertContext createInsertContext(Document source) {
+		return createInsertContext(MappedDocument.of(source));
+	}
+
+	InsertContext createInsertContext(MappedDocument mappedDocument) {
+		return new InsertContext(mappedDocument);
+	}
+
 	/**
 	 * Create a new {@link QueryContext} instance.
 	 *
@@ -227,6 +236,57 @@ AggregationDefinition createAggregation(Aggregation aggregation,
 		return new AggregationDefinition(aggregation, aggregationOperationContext);
 	}
 
+	/**
+	 * {@link InsertContext} encapsulates common tasks required to interact with {@link Document} to be inserted.
+	 *
+	 * @since 3.4.1
+	 */
+	class InsertContext {
+
+		private final MappedDocument source;
+
+		private InsertContext(MappedDocument source) {
+			this.source = source;
+		}
+
+		/**
+		 * Prepare the {@literal _id} field. May generate a new {@literal id} value and convert it to the id properties
+		 * {@link MongoPersistentProperty#getFieldType() target type}.
+		 *
+		 * @param type must not be {@literal null}.
+		 * @param <T>
+		 * @return the {@link MappedDocument} containing the changes.
+		 * @see #prepareId(MongoPersistentEntity)
+		 */
+		<T> MappedDocument prepareId(Class<T> type) {
+			return prepareId(mappingContext.getPersistentEntity(type));
+		}
+
+		/**
+		 * Prepare the {@literal _id} field. May generate a new {@literal id} value and convert it to the id properties
+		 * {@link MongoPersistentProperty#getFieldType() target type}.
+		 *
+		 * @param entity can be {@literal null}.
+		 * @param <T>
+		 * @return the {@link MappedDocument} containing the changes.
+		 */
+		<T> MappedDocument prepareId(@Nullable MongoPersistentEntity<T> entity) {
+
+			if (entity == null) {
+				return source;
+			}
+
+			MongoPersistentProperty idProperty = entity.getIdProperty();
+			if (idProperty != null
+					&& (idProperty.hasExplicitWriteTarget() || idProperty.isAnnotationPresent(MongoId.class))) {
+				if (!ClassUtils.isAssignable(ObjectId.class, idProperty.getFieldType())) {
+					source.updateId(queryMapper.convertId(new ObjectId(), idProperty.getFieldType()));
+				}
+			}
+			return source;
+		}
+	}
+
 	/**
 	 * {@link QueryContext} encapsulates common tasks required to convert a {@link Query} into its MongoDB document
 	 * representation, mapping field names, as well as determining and applying {@link Collation collations}.
@@ -288,8 +348,7 @@ <T> Document getMappedQuery(@Nullable MongoPersistentEntity<T> entity) {
 			return queryMapper.getMappedObject(getQueryObject(), entity);
 		}
 
-		Document getMappedFields(@Nullable MongoPersistentEntity<?> entity,
-				EntityProjection<?, ?> projection) {
+		Document getMappedFields(@Nullable MongoPersistentEntity<?> entity, EntityProjection<?, ?> projection) {
 
 			Document fields = evaluateFields(entity);
 
@@ -402,8 +461,7 @@ private DistinctQueryContext(@Nullable Object query, String fieldName) {
 		}
 
 		@Override
-		Document getMappedFields(@Nullable MongoPersistentEntity<?> entity,
-				EntityProjection<?, ?> projection) {
+		Document getMappedFields(@Nullable MongoPersistentEntity<?> entity, EntityProjection<?, ?> projection) {
 			return getMappedFields(entity);
 		}
 

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

@@ -1403,7 +1403,8 @@ protected Mono<Object> insertDocument(String collectionName, Document dbDoc, Cla
 					.format("Inserting Document containing fields: " + dbDoc.keySet() + " in collection: " + collectionName));
 		}
 
-		Document document = new Document(dbDoc);
+		MappedDocument document = MappedDocument.of(dbDoc);
+		queryOperations.createInsertContext(document).prepareId(entityClass);
 
 		Flux<InsertOneResult> execute = execute(collectionName, collection -> {
 
@@ -1413,10 +1414,10 @@ protected Mono<Object> insertDocument(String collectionName, Document dbDoc, Cla
 
 			MongoCollection<Document> collectionToUse = prepareCollection(collection, writeConcernToUse);
 
-			return collectionToUse.insertOne(document);
+			return collectionToUse.insertOne(document.getDocument());
 		});
 
-		return Flux.from(execute).last().map(success -> MappedDocument.of(document).getId());
+		return Flux.from(execute).last().map(success -> document.getId());
 	}
 
 	protected Flux<ObjectId> insertDocumentList(String collectionName, List<Document> dbDocList) {
@@ -1480,7 +1481,7 @@ protected Mono<Object> saveDocument(String collectionName, Document document, Cl
 
 			Publisher<?> publisher;
 			if (!mapped.hasId()) {
-				publisher = collectionToUse.insertOne(document);
+				publisher = collectionToUse.insertOne(queryOperations.createInsertContext(mapped).prepareId(entityClass).getDocument());
 			} else {
 
 				MongoPersistentEntity<?> entity = mappingContext.getPersistentEntity(entityClass);

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

@@ -42,6 +42,7 @@
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
+import org.bson.Document;
 import org.bson.types.ObjectId;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
@@ -3635,6 +3636,38 @@ public void saveAndLoadStringThatIsAnObjectIdAsString() {
 		assertThat(target).isEqualTo(source);
 	}
 
+	@Test // GH-4026
+	void saveShouldGenerateNewIdOfTypeIfExplicitlyDefined() {
+
+		RawStringId source = new RawStringId();
+		source.value = "new value";
+
+		template.save(source);
+
+		template.execute(RawStringId.class, collection -> {
+
+			org.bson.Document first = collection.find(new org.bson.Document()).first();
+			assertThat(first.get("_id")).isInstanceOf(String.class);
+			return null;
+		});
+	}
+
+	@Test // GH-4026
+	void insertShouldGenerateNewIdOfTypeIfExplicitlyDefined() {
+
+		RawStringId source = new RawStringId();
+		source.value = "new value";
+
+		template.insert(source);
+
+		template.execute(RawStringId.class, collection -> {
+
+			org.bson.Document first = collection.find(new org.bson.Document()).first();
+			assertThat(first.get("_id")).isInstanceOf(String.class);
+			return null;
+		});
+	}
+
 	@Test // DATAMONGO-2193
 	public void shouldNotConvertStringToObjectIdForNonIdField() {