Fix @MongoId mapping for insertAll.

This commit fixes an issue where id properties annotated with MongoId had not been converted into the desired target type when inserting a collection of objects instead a single one.

Resolves: #4944
Original pull request: #4945

Author: christophstrobl

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

@@ -1475,7 +1475,10 @@ protected <T> Collection<T> doInsertBatch(String collectionName, Collection<? ex
 			maybeEmitEvent(new BeforeSaveEvent<>(initialized, document, collectionName));
 			initialized = maybeCallBeforeSave(initialized, document, collectionName);
 
-			documentList.add(document);
+			MappedDocument mappedDocument = queryOperations.createInsertContext(MappedDocument.of(document))
+				.prepareId(uninitialized.getClass());
+
+			documentList.add(mappedDocument.getDocument());
 			initializedBatchToSave.add(initialized);
 		}
 

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

@@ -34,6 +34,7 @@
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
+import org.bson.Document;
 import org.bson.types.ObjectId;
 import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
@@ -3110,6 +3111,18 @@ public void generatesIdForInsertAll() {
 		assertThat(jesse.getId()).isNotNull();
 	}
 
+	@Test // GH-4944
+	public void insertAllShouldConvertIdToTargetTypeBeforeSave() {
+
+		RawStringId walter = new RawStringId();
+		walter.value = "walter";
+
+		RawStringId returned = template.insertAll(List.of(walter)).iterator().next();
+		org.bson.Document document = template.execute(RawStringId.class, collection -> collection.find().first());
+
+		assertThat(returned.id).isEqualTo(document.get("_id"));
+	}
+
 	@Test // DATAMONGO-1208
 	public void takesSortIntoAccountWhenStreaming() {