How do you return null from a @BatchMapping? #1136
Description
I've been trying to implement a controller which has a BatchMapping with a null value in the list being returned. Behind the scenes, this library is using reactive streams (flux/mono) which doesn't allow you to return a stream that has a null value.
What is the best way to return an optional relationship in the schema?
If you add the following test to the BatchLoadingTests file, you can reproduce the issue.
@Test
void batchLoaderWithNullValue() {
String document = "{ " +
" booksByCriteria(criteria: {author:\"Orwell\"}) { " +
" author {" +
" firstName, " +
" lastName " +
" }" +
" }" +
"}";
this.registry.forTypePair(Long.class, Author.class)
.registerBatchLoader((ids, env) -> Flux.fromIterable(ids.stream().<Author>map(id -> null).toList()));
TestExecutionGraphQlService service = GraphQlSetup.schemaResource(BookSource.schema)
.queryFetcher("booksByCriteria", env -> {
Map<String, Object> criteria = env.getArgument("criteria");
String authorName = (String) criteria.get("author");
return BookSource.findBooksByAuthor(authorName).stream()
.map(book -> new Book(book.getId(), book.getName(), book.getAuthorId()))
.collect(Collectors.toList());
})
.dataFetcher("Book", "author", env -> {
Book book = env.getSource();
DataLoader<Long, Author> dataLoader = env.getDataLoader(Author.class.getName());
return dataLoader.load(book.getAuthorId());
})
.dataLoaders(this.registry)
.toGraphQlService();
Mono<ExecutionGraphQlResponse> responseMono = service.execute(document);
List<Book> books = ResponseHelper.forResponse(responseMono).toList("booksByCriteria", Book.class);
assertThat(books).hasSize(2);
Author author = books.get(0).getAuthor();
assertThat(author).isNull();
}