我正在尝试使用async / await来获取服务，但是第二个服务返回并没有填充我的变量

Question

I have a service to get a list from server. But in this list I need to call another service to return the logo img, the service return ok, but my list remains empty. What i'm did wrong ?

I tried to use async/await in both services I tried to use a separate function to get the logos later, but my html don't change.

 async getOpportunitiesByPage(_searchQueryAdvanced: any = 'active:true') {
    this.listaOportunidades = await this._opportunities
      .listaOportunidades(this.pageSize, this.currentPage, _searchQueryAdvanced)
      .toPromise()
      .then(result => {
        this.totalSize = result['totalElements'];
        return result['content'].map(async (opportunities: any) => {
          opportunities.logoDesktopUrl = await this.getBrand(opportunities['brandsUuid']);
          console.log(opportunities.logoDesktopUrl);
          return { opportunities };
        });
      });

    this.getTasks(this.totalSize);
  }

No errors, just my html don't change. in my console.log(opportunities.logoDesktopUrl); return undefined

but in the end return filled.

info: Angular 7 server amazon aws.

Answer 1

await is used to wait for promise .

You should return promise from getBrand if you want to wait for it in getOpportunitiesByPage .

Change the getBrand function as following.

getBrand(brandsUuid): Observable<string> {
  this.brandService.getById(brandsUuid).pipe(map(res => { 
    console.log(res.logoDesktopUrl); return res.logoDesktopUrl;
  }))
}

Change opportunities.logoDesktopUrl = await this.getBrand(opportunities['brandsUuid']); to opportunities.logoDesktopUrl = await this.getBrand(opportunities['brandsUuid']).toPromise();

Please make sure you imported map from rxjs/operators .

Answer 2

At first,when you await , you should not use then .

At second, async/await runs only with Promises.

async getOpportunitiesByPage(_searchQueryAdvanced: any = 'active:true') {
  const result = await this._opportunities
    .listaOportunidades(this.pageSize, this.currentPage, _searchQueryAdvanced)
    .toPromise();
  this.totalSize = result['totalElements'];
  this.listaOportunidades = result['content'].map(async (opportunities: any) => {
    opportunities.logoDesktopUrl = await this.getBrand(opportunities['brandsUuid']);
    console.log(opportunities.logoDesktopUrl);
    return opportunities;
  });

  this.getTasks(this.totalSize);
}

getBrand(brandsUuid) { 
  return new Promise((resolve, reject) => {
    this.brandService.getById(brandsUuid).subscribe(res => { 
      console.log(res.logoDesktopUrl);
      return resolve(res.logoDesktopUrl);
    }, err => {
      return reject(err);
    });
  });
}

But, because rxjs is a used in Angular, you should use it instead of async/await :

getOpportunitiesByPage: void(_searchQueryAdanced: any = 'active:true') {
  this._opportunities.listaOportunidades(this.pageSize, this.currentPage, _searchQueryAdvanced).pipe(
    tap(result => {
      // we do that here because the original result will be "lost" after the next 'flatMap' operation
      this.totalSize = result['totalElements'];
    }),
    // first, we create an array of observables then flatten it with flatMap
    flatMap(result => result['content'].map(opportunities => this.getBrand(opportunities['brandsUuid']).pipe(
        // merge logoDesktopUrl into opportunities object
        map(logoDesktopUrl => ({...opportunities, ...{logoDesktopUrl}}))
      )
    ),
    // then we make each observable of flattened array complete
    mergeAll(),
    // then we wait for each observable to complete and push each result in an array
    toArray()
  ).subscribe(
    opportunitiesWithLogoUrl => { 
      this.listaOportunidades = opportunitiesWithLogoUrl;
      this.getTasks(this.totalSize);
    }, err => console.log(err)
  );
}

getBrand(brandsUuid): Observable<string> {
  return this.brandService.getById(brandsUuid).pipe(
    map(res => res.logoDesktopUrl)
  );
}

Here is a working example on stackblittz

There might be a simpler way to do it but it runs :-)