Allow non-nullable types in GraphQL Relay

Closes gh-1173

Signed-off-by: James Bodkin <[email protected]>
[[email protected]: remove unrelated test]
Signed-off-by: Brian Clozel <[email protected]>

Author: James Bodkin

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

@@ -39,7 +39,6 @@
 import graphql.schema.GraphQLList;
 import graphql.schema.GraphQLNonNull;
 import graphql.schema.GraphQLObjectType;
-import graphql.schema.GraphQLOutputType;
 import graphql.schema.GraphQLSchemaElement;
 import graphql.schema.GraphQLType;
 import graphql.schema.GraphQLTypeVisitorStub;
@@ -153,7 +152,7 @@ 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 (unwrapNonNullType(listType.getWrappedType()) instanceof GraphQLObjectType type) {
 				return type;
 			}
 		}
@@ -165,7 +164,14 @@ private static GraphQLType getType(@Nullable GraphQLFieldDefinition field) {
 		if (field == null) {
 			return null;
 		}
-		GraphQLOutputType type = field.getType();
+		return unwrapNonNullType(field.getType());
+	}
+
+	@Nullable
+	private static GraphQLType unwrapNonNullType(@Nullable GraphQLType type) {
+		if (type == null) {
+			return null;
+		}
 		return (type instanceof GraphQLNonNull nonNullType) ? nonNullType.getWrappedType() : type;
 	}
 
@@ -184,14 +190,16 @@ public static ConnectionFieldTypeVisitor create(List<ConnectionAdapter> adapters
 
 	/**
 	 * {@code DataFetcher} decorator that adapts return values with an adapter.
+	 * @param delegate the datafetcher delegate
+	 * @param adapter the connection adapter to use
 	 */
-	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");
 		}

Diff for: 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;