Allow non-nullable types in graphql relay

Author: James Bodkin

spring-graphql/src/main/java/org/springframework/graphql/data/pagination/ConnectionFieldTypeVisitor.java

@@ -153,7 +153,7 @@ private static GraphQLObjectType getAsObjectType(@Nullable GraphQLFieldDefinitio
 	@Nullable
 	private static GraphQLObjectType getEdgeType(@Nullable GraphQLFieldDefinition field) {
 		if (getType(field) instanceof GraphQLList listType) {
-			if (listType.getWrappedType() instanceof GraphQLObjectType type) {
+			if (getType(listType.getWrappedType()) instanceof GraphQLObjectType type) {
 				return type;
 			}
 		}
@@ -169,6 +169,14 @@ private static GraphQLType getType(@Nullable GraphQLFieldDefinition field) {
 		return (type instanceof GraphQLNonNull nonNullType) ? nonNullType.getWrappedType() : type;
 	}
 
+	@Nullable
+	private static GraphQLType getType(@Nullable GraphQLType type) {
+		if (type == null) {
+			return null;
+		}
+		return (type instanceof GraphQLNonNull nonNullType) ? nonNullType.getWrappedType() : type;
+	}
+
 
 	/**
 	 * Create a {@code ConnectionTypeVisitor} instance that delegates to the
@@ -185,13 +193,13 @@ public static ConnectionFieldTypeVisitor create(List<ConnectionAdapter> adapters
 	/**
 	 * {@code DataFetcher} decorator that adapts return values with an adapter.
 	 */
-	private record ConnectionDataFetcher(DataFetcher<?> delegate, ConnectionAdapter adapter) implements DataFetcher<Object> {
+	record ConnectionDataFetcher(DataFetcher<?> delegate, ConnectionAdapter adapter) implements DataFetcher<Object> {
 
 		private static final Connection<?> EMPTY_CONNECTION =
 				new DefaultConnection<>(Collections.emptyList(), new DefaultPageInfo(null, null, false, false));
 
 
-		private ConnectionDataFetcher {
+		ConnectionDataFetcher {
 			Assert.notNull(delegate, "DataFetcher delegate is required");
 			Assert.notNull(adapter, "ConnectionAdapter is required");
 		}

spring-graphql/src/test/java/org/springframework/graphql/data/pagination/ConnectionFieldTypeVisitorTests.java

@@ -205,6 +205,44 @@ void connectionTypeWithoutEdgesIsNotDecorated() throws Exception {
 			assertThat(actual).isSameAs(dataFetcher);
 		}
 
+		@Test
+		void connectionTypeWithNonNullEdgesIsDecorated() throws Exception {
+			String schemaContent = """
+					type Query {
+						libraries(first: Int, after: String, last: Int, before: String): LibraryConnection!
+					}
+
+					type LibraryConnection {
+						edges: [LibraryEdge!]!
+						pageInfo: PageInfo!
+					}
+
+					type LibraryEdge {
+						node: Library!
+						cursor: String!
+					}
+
+					type Library {
+						name: String
+					}
+
+					type PageInfo {
+						hasPreviousPage: Boolean!
+						hasNextPage: Boolean!
+						startCursor: String
+						endCursor: String
+					}
+					""";
+
+			FieldCoordinates coordinates = FieldCoordinates.coordinates("Query", "libraries");
+			DataFetcher<?> dataFetcher = env -> null;
+
+			DataFetcher<?> actual =
+					applyConnectionFieldTypeVisitor(schemaContent, coordinates, dataFetcher);
+
+			assertThat(actual).isInstanceOf(ConnectionFieldTypeVisitor.ConnectionDataFetcher.class);
+		}
+
 		private static DataFetcher<?> applyConnectionFieldTypeVisitor(
 				Object schemaSource, FieldCoordinates coordinates, DataFetcher<?> fetcher) throws Exception {
 
@@ -291,8 +329,6 @@ public TraversalControl visitGraphQLFieldDefinition(GraphQLFieldDefinition node,
 		}
 	}
 
-
-
 	private static class ListConnectionAdapter implements ConnectionAdapter {
 
 		private int initialOffset = 0;

spring-graphql/src/test/java/org/springframework/graphql/execution/BatchLoadingTests.java

@@ -88,4 +88,43 @@ void batchLoader() {
 		assertThat(author.getLastName()).isEqualTo("Orwell");
 	}
 
+	@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();
+	}
+
 }