Minor optimization in QuerydslDataFetcher

Use single MultiValueMap in method that flattens arguments vs
creating a new one at each level of recursion.

See gh-1085

Author: rstoyanchev

spring-graphql/src/main/java/org/springframework/graphql/data/query/QuerydslDataFetcher.java

@@ -143,33 +143,29 @@ public String getDescription() {
 	 * @return the resulting predicate
 	 */
 	protected Predicate buildPredicate(DataFetchingEnvironment environment) {
-		MultiValueMap<String, Object> parameters = new LinkedMultiValueMap<>();
 		QuerydslBindings bindings = new QuerydslBindings();
-
 		EntityPath<?> path = SimpleEntityPathResolver.INSTANCE.createPath(this.domainType.getType());
 		this.customizer.customize(bindings, path);
 
-		parameters.putAll(flatten(null, getArgumentValues(environment)));
+		MultiValueMap<String, Object> parameters = new LinkedMultiValueMap<>();
+		addParameters(null, getArgumentValues(environment), parameters);
 
 		return BUILDER.getPredicate(this.domainType, parameters, bindings);
 	}
 
 	@SuppressWarnings("unchecked")
-	private MultiValueMap<String, Object> flatten(@Nullable String prefix, Map<String, Object> inputParameters) {
-		MultiValueMap<String, Object> parameters = new LinkedMultiValueMap<>();
+	private void addParameters(
+			@Nullable String prefix, Map<String, Object> arguments, MultiValueMap<String, Object> parameters) {
 
-		for (Map.Entry<String, Object> entry : inputParameters.entrySet()) {
+		for (Map.Entry<String, Object> entry : arguments.entrySet()) {
 			Object value = entry.getValue();
 			if (value instanceof Map<?, ?> nested) {
-				parameters.addAll(flatten(entry.getKey(), (Map<String, Object>) nested));
-			}
-			else {
-				List<Object> values = (value instanceof List) ? (List<Object>) value : Collections.singletonList(value);
-				parameters.put(((prefix != null) ? prefix + "." : "") + entry.getKey(), values);
+				addParameters(entry.getKey(), (Map<String, Object>) nested, parameters);
+				continue;
 			}
+			List<Object> values = (value instanceof List) ? (List<Object>) value : Collections.singletonList(value);
+			parameters.put(((prefix != null) ? prefix + "." : "") + entry.getKey(), values);
 		}
-
-		return parameters;
 	}
 
 	/**

spring-graphql/src/test/java/org/springframework/graphql/data/query/QuerydslDataFetcherTests.java

@@ -346,13 +346,13 @@ void shouldNestForSingleArgumentInputType() {
 		assertThat(books.get(0).getName()).isEqualTo(book1.getName());
 	}
 
-	@Test
+	@Test // gh-1081
 	void shouldConsiderNestedArguments() {
 		Book book1 = new Book(42L, "Hitchhiker's Guide to the Galaxy", new Author(0L, "Douglas", "Adams"));
 		Book book2 = new Book(53L, "Breaking Bad", new Author(0L, "", "Heisenberg"));
 		mockRepository.saveAll(Arrays.asList(book1, book2));
 
-		String queryName = "booksByNestableCriteria";
+		String queryName = "booksByNestedCriteria";
 
 		Mono<ExecutionGraphQlResponse> responseMono =
 				graphQlSetup(queryName, QuerydslDataFetcher.builder(mockRepository).many())

spring-graphql/src/test/resources/books/schema.graphqls

@@ -2,7 +2,7 @@ type Query {
     bookById(id: ID): Book
     booksById(id: [ID]): [Book]
     books(id: ID, name: String, author: String): [Book!]!
-    booksByNestableCriteria(id: ID, name: String, author: AuthorCriteria): [Book!]!
+    booksByNestedCriteria(id: ID, name: String, author: AuthorCriteria): [Book!]!
     booksByCriteria(criteria:BookCriteria): [Book]
     booksByProjectedArguments(name: String, author: String): [Book]
     booksByProjectedCriteria(criteria:BookCriteria): [Book]