A cascading call means that based on what call is happening another call should take place and possibly another one based on that.
A dependant call means the calls needs to happen in order. Call 2 must happen after Call 1 has returned. It might even be possible that Call2 needs be specified using data from Call 1.
Imagine you have the following scenario:
login()
.then(getUserDetails)
.then(getOrdersByUser)
import { of, from } from 'rxjs';
import { switchMap } from 'rxjs/operators';
let stream$ = of({ message : 'Logged in' }).pipe(
switchMap( result => {
return of({ id: 1, name : 'user' })
}),
switchMap((user) => {
return from(
[{ id: 114, userId : 1 },
{ id: 117, userId : 1 } ])
})
);
stream$.subscribe((orders) => {
console.log('Orders', orders);
})
// Array of orders
I've simplified this one a bit in the Rxjs example but imagine instead of
of()
it does the proper ajax() call like in Operators and Ajax
getUser()
.then((user) => {
return Promise.all(
getOrders(),
getMessages()
)
})
import { of } from 'rxjs';
import { switchMap, forkJoin } from 'rxjs/operators';
let stream$ = of({ id : 1, name : 'User' })
stream.pipe(
switchMap((user) => {
return forkJoin(
from([{ id : 114, user: 1}, { id : 115, user: 1}],
from([{ id : 200, user: 1}, { id : 201, user: 1}])
)
})
);
stream$.subscribe((result) => {
console.log('Orders', result[0]);
console.log('Messages', result[1]);
})
We are doing switchMap() instead of flatMap() so we can abandon an ajax call if necessary, this will make more sense in Auto complete recipe