CODEWITHSUNDEEP
javascriptrxjsangular-httpclientrxjs-observables
luca.vercelli
luca.vercelli

Reputation: 1038

Feed an observable with two more observables

I have a scenario with 3 webservices, say A, B and C.

A and B can be invoked without arguments. C requires parameters deriving from both A and B. For example:

   http.get("A").subscribe(x => console.log(x))
   // prints 'goofy'
   http.get("B").subscribe(y => console.log(y))
   // prints 'mickey'
   http.get("C?param1=goofy&param2=mickey").subscribe(z => console.log(z))
   // prints 'daisy'

I wonder how to create a single Observable that does the job, and whose subscription return the result from webservice C.

  obs1 = http.get("A")
  obs2 = http.get("B")
  f3 = (x,y => http.get("C?param1="+x+"&param2="+y))
  bigObservable = someconcatenationof(obs1, obs2, f3)

and I would like that

  bigObservable.subscribe(z => console.log(z))
  // should print "daisy"

I suppose that this question can be a little bit generalized: A, B, C do not need to be webservices, they can just be some kind of Observable's, where C's constructor requires results from both A and B.

Upvotes: 0

Views: 48

Answers (1)

Andrei Gătej
Andrei Gătej

Reputation: 11934

I think this would be one approach:

forkJoin({
  a: http.get("A"),
  b: http.get("B"),
}).pipe(
  mergeMap(({ a, b }) => http.get(`C?param1=${a}&param2=${b}`))
)

forkJoin will subscribe to all the provided observables at the same time and will emit their last values when all of them complete.

Upvotes: 4

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