angular 英雄之旅 - 步骤 8/HTTP - 内存中的 webapi 返回未定义

Question

问题：内存中的网络 api 会 return 'undefined' 当尝试使用 HeroService.getHeroes() 获取所有英雄时，如本教程第 8 步所述.

InMemoryDataService 实现：

import { InMemoryDbService } from 'angular-in-memory-web-api';
import { Hero } from './hero';

export class InMemoryDataService implements InMemoryDbService {
  createDb() {
    // This constant has a LOWERCASE name in the tutorial. 
    // The code below is copied-pasted from the mock-heroes service file.

    const HEROES = [
      { id: 11, name: 'Mr. Nice' },
      { id: 12, name: 'Narco' },
      { id: 13, name: 'Bombasto' },
      { id: 14, name: 'Celeritas' },
      { id: 15, name: 'Magneta' },
      { id: 16, name: 'RubberMan' },
      { id: 17, name: 'Dynama' },
      { id: 18, name: 'Dr IQ' },
      { id: 19, name: 'Magma' },
      { id: 20, name: 'Tornado' }
    ];
    return { HEROES };
  }
  genId(heroes: Hero[]): number {
    return heroes.length > 0 ? Math.max(...heroes.map(hero => hero.id)) + 1 : 11;
  }
  constructor() { }
}

使用 HTTP 的 HeroesService 实现（与当前问题相关的摘录）

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { Hero } from './hero';
import { Observable, of } from 'rxjs';
import { catchError, map, tap } from 'rxjs/operators';
import { MessageService } from './message.service';

@Injectable({
  providedIn: 'root'
})
export class HeroService {
  private heroesUrl = 'api/heroes';
  getHero(id: number): Observable<Hero> {
    const url = `${this.heroesUrl}/${id}`;
    return this.http.get<Hero>(url).pipe(
      tap(_ => this.log(`fetched hero id=${id}`)),
      catchError(this.handleError<Hero>(`getHero id =${id}`))
    );
  }
  getHeroes(): Observable<Hero[]> {
    return this.http.get<Hero[]>(this.heroesUrl)
      .pipe(
        tap(heroes => this.log('fetched heroes')),
        catchError(this.handleError('getHeroes', [])));
  }
  /**
   * Handle Http operation that failed.
   * Let the app continue.
   * @param operation - name of the operation that failed
   * @param result - optional value to return as the observable result
   */
  handleError<T>(operation = 'operation', result?: T): any {
    return (error: any): Observable<T> => {
      // TODO send the error to remote logging infrastructure
      console.error(error);
      this.log(`${operation} failed: ${error.message}`);
      // Let the app keep running by returning an empty result
      return of(result as T);
    };
  }

  private log(message: string) {
    this.messageService.add(`HeroService: ${message}`);
  }
  constructor(private http: HttpClient, private messageService: MessageService) { }
}

package.json:

{
  "name": "angular-tour-of-heroes",
  "version": "0.0.0",
  "scripts": {
    "ng": "ng",
    "start": "ng serve --open",
    "build": "ng build",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },
  "private": true,
  "dependencies": {
    "@angular/animations": "^6.1.0",
    "@angular/common": "^6.1.0",
    "@angular/compiler": "^6.1.0",
    "@angular/core": "^6.1.0",
    "@angular/forms": "^6.1.0",
    "@angular/http": "^6.1.0",
    "@angular/platform-browser": "^6.1.0",
    "@angular/platform-browser-dynamic": "^6.1.0",
    "@angular/router": "^6.1.0",
    "angular-in-memory-web-api": "^0.6.1",
    "core-js": "^2.5.4",
    "rxjs": "^6.0.0",
    "zone.js": "~0.8.26"
  },
  "devDependencies": {
    "@angular-devkit/build-angular": "~0.7.0",
    "@angular/cli": "~6.1.5",
    "@angular/compiler-cli": "^6.1.0",
    "@angular/language-service": "^6.1.0",
    "@types/jasmine": "~2.8.6",
    "@types/jasminewd2": "~2.0.3",
    "@types/node": "~8.9.4",
    "codelyzer": "~4.2.1",
    "jasmine-core": "~2.99.1",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "~1.7.1",
    "karma-chrome-launcher": "~2.2.0",
    "karma-coverage-istanbul-reporter": "~2.0.0",
    "karma-jasmine": "~1.1.1",
    "karma-jasmine-html-reporter": "^0.2.2",
    "protractor": "~5.4.0",
    "ts-node": "~5.0.1",
    "tslint": "~5.9.1",
    "typescript": "~2.7.2"
  }
}

运行应用程序时的错误消息：

HeroService: getHeroes failed: undefined

为什么内存中的网络 api 无法将对 'api/heroes' 的请求映射到我的数据？

Answer 1

TL;DR：您在 InMemoryDataService 实现中定义的 constants/properties 必须与您的 API (see end of paragraph 'HTTP request handling' and next paragraph) 的资源 URI 相匹配。考虑了大小写（请参阅实施中的评论），这是问题中报告的意外错误的原因。

修复了 InMemoryDataService 实现（带有注释）：

import { InMemoryDbService } from 'angular-in-memory-web-api';
import { Hero } from './hero';

export class InMemoryDataService implements InMemoryDbService {
  createDb() {
    // SOLUTION & EXPLANATION
    // this constant has to have the same name as the resource url the in-memory service will be invoked with.
    // e.g.  heroes2 => api/heroes2
    // note: do not forget that urls are case-sensitive ;) (see 
    const heroes = [
      { id: 11, name: 'Mr. Nice' },
      { id: 12, name: 'Narco' },
      { id: 13, name: 'Bombasto' },
      { id: 14, name: 'Celeritas' },
      { id: 15, name: 'Magneta' },
      { id: 16, name: 'RubberMan' },
      { id: 17, name: 'Dynama' },
      { id: 18, name: 'Dr IQ' },
      { id: 19, name: 'Magma' },
      { id: 20, name: 'Tornado' }
    ];
    return { heroes };
  }
  genId(heroes: Hero[]): number {
    return heroes.length > 0 ? Math.max(...heroes.map(hero => hero.id)) + 1 : 11;
  }
  constructor() { }
}

angular 英雄之旅 - 步骤 8/HTTP - 内存中的 webapi 返回未定义

angular tour of heroes - step 8/HTTP - in-memory webapi returning undefined

in-memory-database

angular-cli

angular

angular-in-memory-web-api