fix(federation): override federated resolveType for interfaces

lib/federation/graphql-federation.factory.ts

@@ -222,7 +222,7 @@ export class GraphQLFederationFactory {
     // Bail if inconsistent with original schema
     if (
       !autoGeneratedType ||
-      !(autoGeneratedType instanceof GraphQLUnionType) ||
+      !(autoGeneratedType instanceof GraphQLUnionType || autoGeneratedType instanceof GraphQLInterfaceType) ||
       !autoGeneratedType.resolveType
     ) {
       return typeInFederatedSchema;

lib/schema-builder/factories/interface-definition.factory.ts

@@ -115,14 +115,15 @@ export class InterfaceDefinitionFactory {
     return () => {
       let fields: GraphQLFieldConfigMap<any, any> = {};
       metadata.properties.forEach((field) => {
+        const type = this.outputTypeFactory.create(
+          field.name,
+          field.typeFn(),
+          options,
+          field.options,
+        );
         fields[field.schemaName] = {
           description: field.description,
-          type: this.outputTypeFactory.create(
-            field.name,
-            field.typeFn(),
-            options,
-            field.options,
-          ),
+          type,
           args: this.argsFactory.create(field.methodArgs, options),
           resolve: (root: object) => {
             const value = root[field.name];
@@ -131,6 +132,15 @@ export class InterfaceDefinitionFactory {
               : value;
           },
           deprecationReason: field.deprecationReason,
+          /**
+           * AST node has to be manually created in order to define directives
+           * (more on this topic here: https://github.com/graphql/graphql-js/issues/1343)
+           */
+          astNode: this.astDefinitionNodeFactory.createFieldNode(
+            field.name,
+            type,
+            field.directives,
+          ),
           extensions: {
             complexity: field.complexity,
             ...field.extensions,

tests/code-first-federation/app.module.ts

@@ -3,11 +3,13 @@ import { GraphQLFederationModule } from '../../lib';
 import { UserModule } from './user/user.module';
 import { PostModule } from './post/post.module';
 import { User } from './user/user.entity';
+import { RecipeModule } from './recipe/recipe.module';
 
 @Module({
   imports: [
     UserModule,
     PostModule,
+    RecipeModule,
     GraphQLFederationModule.forRoot({
       debug: false,
       autoSchemaFile: true,

tests/code-first-federation/recipe/irecipe.resolver.ts

@@ -0,0 +1,10 @@
+import { Query, Resolver } from '../../../lib';
+import { IRecipe } from './recipe';
+
+@Resolver((of) => IRecipe)
+export class IRecipeResolver {
+  @Query((returns) => IRecipe)
+  public recipe() {
+    return { id: '1', title: 'Recipe', description: 'Interface description' }
+  }
+}

tests/code-first-federation/recipe/recipe.module.ts

@@ -0,0 +1,7 @@
+import { Module } from '@nestjs/common';
+import { IRecipeResolver } from './irecipe.resolver';
+
+@Module({
+  providers: [IRecipeResolver],
+})
+export class RecipeModule {}

tests/code-first-federation/recipe/recipe.ts

@@ -0,0 +1,33 @@
+import {
+  Directive,
+  Field,
+  ID,
+  InterfaceType,
+  ObjectType,
+} from '../../../lib';
+
+@InterfaceType()
+export abstract class Base {
+  @Field((type) => ID)
+  id: string;
+}
+
+@InterfaceType({
+  resolveType: (value) => {
+    return Recipe;
+  },
+})
+export abstract class IRecipe extends Base {
+  @Field()
+  title: string;
+
+  @Field()
+  @Directive('@external')
+  externalField: string;
+}
+
+@ObjectType({ implements: IRecipe })
+export class Recipe extends IRecipe {
+  @Field()
+  description: string;
+}

tests/e2e/code-first-federation.spec.ts

@@ -32,7 +32,7 @@ describe('Code-first - Federation', () => {
     expect(response.data).toEqual({
       _service: {
         sdl:
-          '"""Search result description"""\nunion FederationSearchResultUnion = Post | User\n\ntype Post @key(fields: "id") {\n  id: ID!\n  title: String!\n  authorId: Int!\n}\n\ntype Query {\n  findPost(id: Float!): Post!\n  getPosts: [Post!]!\n  search: [FederationSearchResultUnion!]! @deprecated(reason: "test")\n}\n\ntype User @extends @key(fields: "id") {\n  id: ID! @external\n  posts: [Post!]!\n}\n',
+          '"""Search result description"""\nunion FederationSearchResultUnion = Post | User\n\ninterface IRecipe {\n  id: ID!\n  title: String!\n  externalField: String! @external\n}\n\ntype Post @key(fields: "id") {\n  id: ID!\n  title: String!\n  authorId: Int!\n}\n\ntype Query {\n  findPost(id: Float!): Post!\n  getPosts: [Post!]!\n  search: [FederationSearchResultUnion!]! @deprecated(reason: "test")\n  recipe: IRecipe!\n}\n\ntype Recipe implements IRecipe {\n  id: ID!\n  title: String!\n  externalField: String! @external\n  description: String!\n}\n\ntype User @extends @key(fields: "id") {\n  id: ID! @external\n  posts: [Post!]!\n}\n',
       },
     });
   });
@@ -67,6 +67,30 @@ describe('Code-first - Federation', () => {
     });
   });
 
+  it(`should return query result`, async () => {
+    const response = await apolloClient.query({
+      query: gql`
+          {
+              recipe {
+                  id
+                  title
+                  ... on Recipe {
+                    description
+                  }
+              }
+          }
+      `,
+    });
+    expect(response.data).toEqual({
+      recipe:
+        {
+          id: '1',
+          title: 'Recipe',
+          description: 'Interface description',
+        },
+    });
+  });
+
   afterEach(async () => {
     await app.close();
   });