如何在第二个请求中使用来自concatMap的第一个响应

Question

I am trying to avoid the nested subscription in request to the backend. I need to login, then get a service token based on the response of the login, then get a encryption token based on the service token.

I have seen about concatMap but i am not sure how to use the first response in the second request or third

  this.rest.CallLogin(this.data).pipe(
            concatMap(serviceToken => this.rest.GetServiceTicket(1stresponse.headers.get('Location'))),// dont know how to get the 1st response from CallLogin
            concatMap(tokenResponse => this.rest.getEncryptToken(serviceToken)),

        );

Answer 1

You can use flatMap in place of the nested subscriptions.

import { flatMap } from 'rxjs/operators';

this.rest.CallLogin(this.data).pipe(
        flatMap((serviceToken) => {
            //serviceToken is the response of first call
            return this.rest.GetServiceTicket(serviceToken.headers.get('Location'))
        }),
        map((tokenResponse) => {
            //tokenResponse is the response of second call
            this.rest.getEncryptToken(tokenResponse)
        });

Answer 2

If i understood correctly then you only want to chain the calls and use the response header from the first response. For that you need to use observe on response in your first call:

this.rest.CallLogin(this.data, {observe: 'response'}).pipe(
    concatMap(loginResponse => this.rest.GetServiceTicket(loginResponse.headers.get('Location'))),
    concatMap(serviceTicket => this.rest.getEncryptToken(serviceTicket)),
);

Answer 3

I ended up using SwitchMap

 this.rest.CallLogin(this.data).pipe(
        switchMap((response: any) => {
        this.data.requestUrl = response.headers.get('Location');
        return this.rest.GetServiceTicket(this.data) // serviceticket
        }),
        switchMap((serviceticket) => {
            return this.rest.getEncryptToken(serviceticket.body) // tokenResponse
        }),
        //continue doing requests or stuff
        switchMap((tokenResponse) => {
            encryptToken = tokenResponse;
            ///...                
        }),