Question

首先，我实际上是刚在Stack Overflow上发帖的，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Apollo服务器能够从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，而NestJS如此相似，因此看起来很合适。

我们遇到的问题是，以下功能似乎无法正常工作： -我想要一个包含服务的模块，该服务可以被赋予许多端点（从uri到微服务） -使用给定的端点，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。 -发生这种情况之后，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）

我已经遍历了官方文档（https://docs.nestjs.com/graphql/quick-start）的示例（https://github.com/nestjs/nest/tree/master/sample/12-graphql-apollo）的示例，当然也检查了github项目（https://github.com/nestjs/graphql）并整理了一下此回购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。

让我从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，目前我有一个如下所示的模式处理程序模块：

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

因此，在这里，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：

    @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);
    }
  };

出于POC的考虑，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，并使其在操场上可见。我们还尝试过让createCountrySchema返回Promise并在调用createGqlOptions中的函数时等待它，但这似乎没有什么作用。

我们得到的实际错误如下：

[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Promise必须通过try / catch进行处理，这样我们才不会收到未处理的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，并且已经看到了许多示例，摘要和讨论，但是我找不到找到缝合远程模式并将其交还给nestjs的示例。 / p>

非常感谢您对此提出的任何评论，特耶德

Answer 1

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

here my code
link for the test

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;
  }

}

Answer 2

这是第一个答案的简化 - 无论在何处调用 GraphQLModule.forRoot(async)（在 appModule 文件中编码或单独导出），下面的代码片段应该会有所帮助

import { GraphQLModule } from "@nestjs/graphql";
import { CommonModule } from "@Common";
import { GraphQLSchema } from 'graphql';
import { ConfigInterface } from "@Common/config/ConfigService";
import {
 stitchSchemas
} from '@graphql-tools/stitch';
import { introspectSchema } from '@graphql-tools/wrap';
import { print } from 'graphql';
import { fetch } from 'cross-fetch';

export default GraphQLModule.forRootAsync({
  imports: [CommonModule],
  useFactory: async (configService: ConfigInterface) => {
    const remoteSchema = await createRemoteSchema('https://countries.trevorblades.com/graphql');
    return {
      playground: process.env.NODE_ENV !== "production",
      context: ({ req, res }) => ({ req, res }),
      installSubscriptionHandlers: true,
      autoSchemaFile: "schema.gql",
      transformSchema : async (schema: GraphQLSchema) => {
        return stitchSchemas({
          subschemas: [
            schema,
            remoteSchema
          ]
        });
      },
    };
  },
});

const createRemoteSchema = async (url : string) =>{
  const executor = async ({ document, variables }) => {
    const query = print(document);
    const fetchResult = await fetch(url, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({ query, variables })
    });
    return fetchResult.json();
  };
  return {
    schema: await introspectSchema(executor),
    executor: executor
  };
}

参考：https://www.graphql-tools.com/docs/stitch-combining-schemas/#stitching-remote-schemas

如何使用Nestjs和Apollo服务器缝合多个远程模式

2 个答案: