Add interface type

graphql_schema/lib/src/gen.dart

@@ -2,11 +2,20 @@ part of graphql_schema.src.schema;
 
 GraphQLObjectType objectType(String name,
     {String description,
+    bool isInterface: false,
     Iterable<GraphQLField> fields = const [],
-        Iterable<GraphQLObjectType> interfaces = const []}) =>
+    Iterable<GraphQLObjectType> interfaces = const []}) {
-    new GraphQLObjectType(name, description)
+  var obj = new GraphQLObjectType(name, description, isInterface: isInterface)
-      ..fields.addAll(fields ?? [])
+    ..fields.addAll(fields ?? []);
-      ..interfaces.addAll(interfaces ?? []);
+
+  if (interfaces?.isNotEmpty == true) {
+    for (var i in interfaces) {
+      obj.inheritFrom(i);
+    }
+  }
+
+  return obj;
+}
 
 GraphQLField<T, Serialized> field<T, Serialized>(String name,
     {Iterable<GraphQLFieldArgument<T, Serialized>> arguments: const [],

graphql_schema/lib/src/object_type.dart

@@ -6,11 +6,27 @@ class GraphQLObjectType
   final String name;
   final String description;
   final List<GraphQLField> fields = [];
+  final bool isInterface;
+
+  final List<GraphQLObjectType> _interfaces = [];
+
+  final List<GraphQLObjectType> _possibleTypes = [];
 
   /// A list of other types that this object type is known to implement.
-  final List<GraphQLObjectType> interfaces = [];
+  List<GraphQLObjectType> get interfaces => new List<GraphQLObjectType>.unmodifiable(_interfaces);
 
-  GraphQLObjectType(this.name, this.description);
+  /// A list of other types that implement this interface.
+  List<GraphQLObjectType> get possibleTypes => new List<GraphQLObjectType>.unmodifiable(_possibleTypes);
+
+  GraphQLObjectType(this.name, this.description, {this.isInterface: false});
+
+  void inheritFrom(GraphQLObjectType other) {
+    if (!_interfaces.contains(other)) {
+      _interfaces.add(other);
+      other._possibleTypes.add(this);
+      other._interfaces.forEach(inheritFrom);
+    }
+  }
 
   @override
   ValidationResult<Map<String, dynamic>> validate(String key, Map input) {
@@ -23,7 +39,8 @@ class GraphQLObjectType
     for (var field in fields) {
       if (field.type is GraphQLNonNullableType) {
         if (!input.containsKey(field.name) || input[field.name] == null) {
-          errors.add('Field "${field.name}, of type ${field.type} cannot be null."');
+          errors.add(
+              'Field "${field.name}, of type ${field.type} cannot be null."');
         }
       }
     }
@@ -56,7 +73,8 @@ class GraphQLObjectType
     return value.keys.fold<Map<String, dynamic>>({}, (out, k) {
       var field = fields.firstWhere((f) => f.name == k, orElse: () => null);
       if (field == null)
-        throw new UnsupportedError('Cannot serialize field "$k", which was not defined in the schema.');
+        throw new UnsupportedError(
+            'Cannot serialize field "$k", which was not defined in the schema.');
       return out..[k.toString()] = field.serialize(value[k]);
     });
   }

graphql_server/lib/introspection.dart

@@ -120,8 +120,11 @@ GraphQLObjectType _reflectSchemaTypes() {
         'possibleTypes',
         type: listType(_reflectSchemaTypes().nonNullable()),
         resolve: (type, _) {
-          // TODO: Interface and union types
+          if (type is GraphQLObjectType && type.isInterface) {
-          return <GraphQLType>[];
+            return type.possibleTypes;
+          } else {
+            return null;
+          }
         },
       ),
     );
@@ -195,7 +198,7 @@ GraphQLObjectType _createTypeType() {
         if (t is GraphQLScalarType)
           return 'SCALAR';
         else if (t is GraphQLObjectType)
-          return 'OBJECT';
+          return t.isInterface ? 'INTERFACE' : 'OBJECT';
         else if (t is GraphQLListType)
           return 'LIST';
         else if (t is GraphQLNonNullableType)
@@ -204,7 +207,7 @@ GraphQLObjectType _createTypeType() {
           return 'ENUM';
         else
           throw new UnsupportedError(
-              'Cannot get the kind of $t.'); // TODO: Interface + union
+              'Cannot get the kind of $t.'); // TODO: union
       },
     ),
     field(
@@ -424,6 +427,14 @@ List<GraphQLType> _fetchAllTypesFromObject(GraphQLObjectType objectType) {
     }
   }
 
+  for (var type in objectType.interfaces) {
+    types.addAll(_fetchAllTypesFromObject(type));
+  }
+
+  for (var type in objectType.possibleTypes) {
+    types.addAll(_fetchAllTypesFromObject(type));
+  }
+
   return types;
 }
 
@@ -440,6 +451,6 @@ Iterable<GraphQLType> _fetchAllTypesFromType(GraphQLType type) {
     types.add(type);
   }
 
-  // TODO: Interface, union
+  // TODO:  union
   return types;
 }