如何使用Spring Data Java更新MongoDB中的嵌套文档

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-mongodb</artifactId>
</dependency>

@Document(collection = "collectionName")
public class ParentDocument {
    @Id
    private String id;
    private String field1;
    private ChildDocument childDocument;
    // getters and setters
}

public class ChildDocument {
    private String field2;
    // getters and setters
}

public interface ParentDocumentRepository extends MongoRepository<ParentDocument, String> {
}

@Autowired
private ParentDocumentRepository parentDocumentRepository;

public void updateNestedDocument(String parentId, String childField2) {
    Optional<ParentDocument> optionalParentDocument = parentDocumentRepository.findById(parentId);
    if (optionalParentDocument.isPresent()) {
        ParentDocument parentDocument = optionalParentDocument.get();
        parentDocument.getChildDocument().setField2(childField2);
        parentDocumentRepository.save(parentDocument);
    }
}