如何使用Nestjs和Apollo服务器缝合多个远程模式

Question

首先，我实际上是在Stack Overflow上发帖的新手，但我当然会尽我所能在此处提供所有相关信息并分享找到的解决方案，因为我可以想象会有更多的人对此感到麻烦。

因此，我们从一个以多个小型微服务为后端的系统开始，我们发现了Apollo服务器，它能够从graphql端点检索模式并将它们缝合在一起，因此我们可以有一个不错的切入点。我们已经可以工作了，但是apollo服务器并没有真正帮助总体架构的工具。那就是我们找到NestJS的原因，因为我们在前端使用了angular，并且NestJS非常相似，因此看起来很合适。

但是，我们遇到的问题是我们似乎无法使以下功能正常工作：-我希望有一个模块，其中包含可以被赋予多个端点（从uri到微服务）的服务-具有这些功能给定的服务应从这些端点检索graphQL模式，并将其制成RemoteExecutableSchemas，然后将它们合并。-合并它们并使用（远程）链接信息制作1个大架构，以便graphQL知道从何处获取数据。-发生这种情况后，我们想添加一些针脚以使所有关系都存在（但这不是我的问题所在）

我一直在浏览官方文档（https://docs.nestjs.com/graphql/quick-start）的示例（https://github.com/nestjs/nest/tree/master/sample/ 12-graphql-apollo），当然也签出了github项目（https://github.com/nestjs/graphql），并在此仓库中整理了一下代码，以查看代码在后台执行的操作。

我们已经尝试了几种方法来即时获取它们，但是无法在实例化之前将模式放入GraphQLModule中。然后，我们认为让服务从端点检索graphqlSchema并使用实际起作用的printSchema（schema）将其写入文件中是可以接受的，但是随后我丢失了链接信息，从而使该信息成为本地模式而不是远程模式。现在，我们提出了以下建议，但再次陷入困境。

让我们从我的package.json中的一个小片段开始，以便人们知道版本:)

"dependencies": {
    "@nestjs/common": "^5.4.0",
    "@nestjs/core": "^5.4.0",
    "@nestjs/graphql": "^5.5.1",
    "apollo-link-http": "^1.5.9",
    "apollo-server-express": "^2.3.2",
    "graphql": "^14.1.1",
    "reflect-metadata": "^0.1.12",
    "rimraf": "^2.6.2",
    "rxjs": "^6.2.2",
    "typescript": "^3.0.1"
  },
  "devDependencies": {
    "@nestjs/testing": "^5.1.0",
    "@types/express": "^4.16.0",
    "@types/jest": "^23.3.1",
    "@types/node": "^10.7.1",
    "@types/supertest": "^2.0.5",
    "jest": "^23.5.0",
    "nodemon": "^1.18.3",
    "prettier": "^1.14.2",
    "supertest": "^3.1.0",
    "ts-jest": "^23.1.3",
    "ts-loader": "^4.4.2",
    "ts-node": "^7.0.1",
    "tsconfig-paths": "^3.5.0",
    "tslint": "5.11.0"
  },

因此，目前我有一个架构处理程序模块，如下所示：

@Module({
  imports: [GraphQLModule.forRootAsync({
    useClass: GqlConfigService
  })],
  controllers: [SchemaHandlerController],
  providers: [SchemaFetcherService, SchemaSticherService, GqlConfigService]
})
export class SchemaHandlerModule {
}

因此，这里我们导入GraphQLModule并让其使用gql-config服务来处理为其提供的GraphQLModuleOptions。

gql-config服务如下所示：

    @Injectable()
export class GqlConfigService implements GqlOptionsFactory {
  async createGqlOptions(): Promise<GqlModuleOptions> {
    try{
      const countrySchema = this.createCountrySchema();
      return {
        typeDefs: [countrySchema]
      };
    } catch(err) {
      console.log(err);
      return {};
    }
  }

所以我异步创建GqlModuleOptions并等待结果。createCountrySchema函数如下所示：

public async createCountrySchema() : GraphQLSchema{
    const uri = 'https://countries.trevorblades.com/Graphql';
    try {
      const link = new HttpLink({
        uri: uri,
        fetch
      });
      const remoteSchema = await introspectSchema(link);

      return makeRemoteExecutableSchema({
        schema: remoteSchema,
        link
      });
    } catch (err) {
      console.log('ERROR: exception when trying to connect to ' + uri + ' Error Message: ' + err);
    }
  };

为了实现POC，我只是获得了一个简单的公共graphQL API作为端点。该函数返回一个GraphQLSchema对象，然后我想将其添加（以某种方式）到GqlOptions中，并使它在操场上可见。我们还尝试过让createCountrySchema返回Promise并在调用createGqlOptions中的函数时等待它，但这似乎没有什么不同。

我们得到的实际错误如下所示：

[Nest] 83   - 2/1/2019, 2:10:57 PM   [RoutesResolver] SchemaHandlerController {/schema-handler}: +1ms
apollo_1  | (node:83) UnhandledPromiseRejectionWarning: Syntax Error: Unexpected [
apollo_1  |
apollo_1  | GraphQL request (2:9)
apollo_1  | 1:
apollo_1  | 2:         [object Promise]
apollo_1  |            ^
apollo_1  | 3:
apollo_1  |
apollo_1  |     at syntaxError (/opt/node_modules/graphql/error/syntaxError.js:24:10)
apollo_1  |     at unexpected (/opt/node_modules/graphql/language/parser.js:1483:33)
apollo_1  |     at parseDefinition (/opt/node_modules/graphql/language/parser.js:155:9)
apollo_1  |     at many (/opt/node_modules/graphql/language/parser.js:1513:16)
apollo_1  |     at parseDocument (/opt/node_modules/graphql/language/parser.js:115:18)
apollo_1  |     at parse (/opt/node_modules/graphql/language/parser.js:50:10)
apollo_1  |     at parseDocument (/opt/node_modules/graphql-tag/src/index.js:129:16)
apollo_1  |     at Object.gql (/opt/node_modules/graphql-tag/src/index.js:170:10)
apollo_1  |     at GraphQLFactory.<anonymous> (/opt/node_modules/@nestjs/graphql/dist/graphql.factory.js:48:55)
apollo_1  |     at Generator.next (<anonymous>)
apollo_1  | (node:83) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)
apollo_1  | (node:83) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

我认为我与这种方法相当接近，但我不确定。我收到的错误指出所有Promises必须使用try / catch进行处理，以便我们不会收到未处理的Promise，我相信我到处都这样做，所以我不知道此错误的来源...

如果有人有任何指示，解决方案或建议，我将非常高兴。一个多星期以来，我一直在努力地使我们想要的功能适合于nestjs，并且已经看到了很多示例，摘要和讨论，但是我找不到能够缝制远程模式并将其交还给nestjs的示例。

特耶德，我谨对此表示任何谢意，

Answer 1

我已经通过使用转换方法解决了模式拼接问题。
看 src/graphql.config/graphql.config.service.ts

这是我的测试代码
链接

import { Injectable } from '@nestjs/common';
import { GqlOptionsFactory, GqlModuleOptions } from '@nestjs/graphql';
import * as ws from 'ws';
import {
  makeRemoteExecutableSchema,
  mergeSchemas,
  introspectSchema
} from 'graphql-tools';
import { HttpLink } from 'apollo-link-http';
import nodeFetch from 'node-fetch';
import { split, from, NextLink, Observable, FetchResult, Operation } from 'apollo-link';
import { getMainDefinition } from 'apollo-utilities';
import { OperationTypeNode, buildSchema as buildSchemaGraphql, GraphQLSchema, printSchema } from 'graphql';
import { setContext } from 'apollo-link-context';
import { SubscriptionClient, ConnectionContext } from 'subscriptions-transport-ws';
import * as moment from 'moment';
import { extend } from 'lodash';

import { ConfigService } from '../config';

declare const module: any;
interface IDefinitionsParams {
  operation?: OperationTypeNode;
  kind: 'OperationDefinition' | 'FragmentDefinition';
}
interface IContext {
  graphqlContext: {
    subscriptionClient: SubscriptionClient,
  };
}

@Injectable()
export class GqlConfigService implements GqlOptionsFactory {

  private remoteLink: string = 'https://countries.trevorblades.com';

  constructor(
    private readonly config: ConfigService
  ) {}

  async createGqlOptions(): Promise<GqlModuleOptions> {
    const remoteExecutableSchema = await this.createRemoteSchema();

    return {
      autoSchemaFile: 'schema.gql',
      transformSchema: async (schema: GraphQLSchema) => {
        return mergeSchemas({
          schemas: [
            schema,
            remoteExecutableSchema
          ]
        });
      },
      debug: true,
      playground: {
        env: this.config.environment,
        endpoint: '/graphql',
        subscriptionEndpoint: '/subscriptions',
        settings: {
          'general.betaUpdates': false,
          'editor.theme': 'dark' as any,
          'editor.reuseHeaders': true,
          'tracing.hideTracingResponse': true,
          'editor.fontSize': 14,
          // tslint:disable-next-line:quotemark
          'editor.fontFamily': "'Source Code Pro', 'Consolas', 'Inconsolata', 'Droid Sans Mono', 'Monaco', monospace",
          'request.credentials': 'include',
        },
      },
      tracing: true,
      installSubscriptionHandlers: true,
      introspection: true,
      subscriptions: {
        path: '/subscriptions',
        keepAlive: 10000,
        onConnect: async (connectionParams, webSocket: any, context) => {
          const subscriptionClient = new SubscriptionClient(this.config.get('HASURA_WS_URI'), {
            connectionParams: {
              ...connectionParams,
              ...context.request.headers
            },
            reconnect: true,
            lazy: true,
          }, ws);

          return {
            subscriptionClient,
          };
        },
        async onDisconnect(webSocket, context: ConnectionContext) {
          const { subscriptionClient } = await context.initPromise;

          if (subscriptionClient) {
            subscriptionClient.close();
          }
        },
      },
      context(context) {
        const contextModified: any = {
          userRole: 'anonymous',
          currentUTCTime: moment().utc().format()
        };

        if (context && context.connection && context.connection.context) {
          contextModified.subscriptionClient = context.connection.context.subscriptionClient;
        }

        return contextModified;
      },
    };
  }

  private wsLink(operation: Operation, forward?: NextLink): Observable<FetchResult> | null {
    const context = operation.getContext();
    const { graphqlContext: { subscriptionClient } }: any = context;
    return subscriptionClient.request(operation);
  }

  private async createRemoteSchema(): Promise<GraphQLSchema> {

    const httpLink = new HttpLink({
      uri: this.remoteLink,
      fetch: nodeFetch as any,
    });

    const remoteIntrospectedSchema = await introspectSchema(httpLink);
    const remoteSchema = printSchema(remoteIntrospectedSchema);
    const link = split(
      ({ query }) => {
        const { kind, operation }: IDefinitionsParams = getMainDefinition(query);
        return kind === 'OperationDefinition' && operation === 'subscription';
      },
      this.wsLink,
      httpLink,
    );

    const contextLink = setContext((request, prevContext) => {
      extend(prevContext.headers, {
        'X-hasura-Role': prevContext.graphqlContext.userRole,
        'X-Hasura-Utc-Time': prevContext.graphqlContext.currentUTCTime,
      });
      return prevContext;
    });

    const buildedHasuraSchema = buildSchemaGraphql(remoteSchema);
    const remoteExecutableSchema = makeRemoteExecutableSchema({
      link: from([contextLink, link]),
      schema: buildedHasuraSchema,
    });

    return remoteExecutableSchema;
  }

}