How to pipe / map an Observable in Angular

问题:

A nested object is showing up as [object Object] so I'm trying to cast it via pipe and map but I'm not getting any where. I've tried the models as classes and interfaces but no help. Can someone tell me what I'm doing wrong? Thanks.

The function:

  getClients(customerId: number): Observable<Client[]> {
    let clientUrl = 'SOME_URL';
    return this.http.get<Client[]>(clientUrl)
      .pipe(map(client: Client) => client.address as Address);
  }

The models:

import { Address } from './address.model';

export class Client{
  id: number;
  name: string;
  accountNumber: string;
  addressId: number;
  phoneNumber: string;
  address: Address;
}


export class Address{
  id: number;
  name: string;
  addressLine1: string;
  addressLine2: string;
  city: string;
  postalCode: string;
}

I'm getting the error: Error TS2345 (TS) Argument of type 'Address' is not assignable to parameter of type 'OperatorFunction<{}, Client[]>'.

回答1:

1) remove the piping part from your getClients() method

2) do the pipe-map before subscribing to getClients() or create another method, that will do only the piping part with the observable returned from getClients()

mapToAddress(): Observable<Address[]> {
  this.getClients.pipe(
    map((clients: Client[]) => clients.map(client => client.address))
  )
}

This is important to understand: when you call .map() method inside .pipe(), you're not getting a single client in this case, you get the whole clients array, pushed to Observable. Because you map the values, that are stored in the Observable - the values of type: < Client[] >.

Your pipe-map would work on some Observable, that emits a single client of type < Client >, not an array.

回答2:

The problem is here:

getClients(customerId: number): Observable<Client[]> {

you requested the function to return in form of observable (array of client) but actually you are returning Observable of Address.

.pipe(map(client: Client) => client.address as Address);

That's why the function is throwing this error. Replace Observable<Client[]> with Observable<Address[]>