如何在Angular2中链接Http调用？

我是Angular2和Http Observable的新手.我有一个调用Http服务并返回Observable的组件.比我订阅Observable,它工作正常.

现在,我希望在该组件中,在调用第一个Http服务之后,如果调用成功,则调用其他Http服务并返回该Observable.因此,如果第一次调用不成功,则组件返回Observable,而它返回Observable的第二次调用.

所以,问题是,链接Http调用的最佳方法是什么？有没有优雅的方式,比如monads？

您可以使用mergeMap操作员执行此操作

首先导入运算符如下:

HttpClientModule

那么这是你如何链接两个电话:

import { mergeMap } from 'rxjs/operators';

this.http.get('./customer.json').pipe(
  mergeMap(customer => this.http.get(customer.contractUrl))
).subscribe(res => this.contract = res);

async getContrat(){
    //get the customer
    const customer = await this.http.get('./customer.json').toPromise();

    //get the contract from url
    const contract = await this.http.get(customer.contractUrl).toPromise();

    return contract; // you can return what you want here
}

this.myService.getContrat().then( (contract) => {
  // do what you want
});

const contract = await this.myService.getContrat();

let customer;
try {
  customer = await this.http.get('./customer.json').toPromise();
}catch(err){
   console.log('Something went wrong will trying to get customer');
   throw err; // propagate the error
   //customer = {};  //it's a possible case
}