CODEWITHSUNDEEP
reactive-programmingrx-android
hguser
hguser

Reputation: 36068

Nested observable in ReactiveX

I have two operation:

  1. Load item from server(the item only contains certain fileds)
  2. Load item from local database(the item in db may contain other fileds)
  3. Combine the item as one update the UI
  4. update item in db

I know how to use rx for each single operation, but once call all of them I only think about nest observable inside other, this will result in callback hell.

What's the right way to complete these jobs?

Upvotes: 0

Views: 509

Answers (1)

yosriz
yosriz

Reputation: 10267

According to your description, Server and local DB query should happen in parallel, after we have both data we combined them, so you need to use zip operator. zip will subscribe to both server and local DB observable, when both Observable emitted values, you'll will get on next with both server and DB data, then combine them in the zip operator func, and you'll get Observable that emits the combined data.

With each emission of combined data (doOnNext), start a save operation in the background, and in the subscriber update the Ui according to the combined data.

Observable<ServerData> getServerData = ...;
Observable<LocalDbData> getLocalDbData = ...;

Observable
    .zip(getServerData, getLocalDbData,
        (serverData, localDbData) -> combinedData(serverData, localDbData))
    .doOnNext(combinedData -> updateDataInDb())
    .subscribe(combinedData -> updateUi(combinedData));

Upvotes: 1

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