CODEWITHSUNDEEP
androidrx-java2
Hector
Hector

Reputation: 5356

How to combine network and database updates in RxJava in Android application

I am investigating the use of RxJava in my latest Android application.

I have a two lists of related updated Database model objects

ListDB1 and ListDB2

the logic I am attempting to implement is as follows

1). For each item in ListDB1
1.1). Transform it to a Network model object
1.2). Execute an Update RESTful API

2). Once all network updates have completed successfully
2.1). Persist ListDB1 to my local database.
2.2). Persist ListDB2 to my local database.

So far I have this code which should call my network API's

    Observable.just(getDatabaseList())
            .subscribeOn(Schedulers.io())
            .flatMapIterable(x -> x)
            .flatMap(database -> transformDatabase(database, DB_1_MAPPER))
            .doOnNext(NetworkController::updateRemote)
            .observeOn(AndroidSchedulers.mainThread())
            .doOnComplete(getOnComplete())
            .doOnError(getOnError())
            .subscribe();

No API calls are executed though

I would rather use Single that Observable as my API calls respond with Single<Response>, however I couldnt see how to achieve Observable.just(<>) with a Single.

Also I cannot see how to commence my Rx process by processing each List item separately for the Network calls, then performing Database calls with a complete list as I am using Realm as my local database which can accept lists of database objects in a single update.

In pseudo code my process resembles:

for each database list item
convert to network model item
call remote update API
When all all network calls are successful
update database with ListDB1
update database with ListDB2
end

Is this possible in one Rx process "stream"?

Upvotes: 0

Views: 462

Answers (1)

Sanlok Lee
Sanlok Lee

Reputation: 3494

1.

I would rather use Single that Observable as my API calls respond with Single, however I couldnt see how to achieve Observable.just(<>) with a Single.

You can do this:

Single.just(getDatabaseList()) // Single<>

However, Single is not suitable in this case because you are not working with a single item, and what you need instead is to iterate through multiple items and work on the items one by one.


2.

processing each List item separately for the Network calls, then performing Database calls with a complete list

You can use toList() operator which emits entire list of items when the observable completes.


3.

The purpose of do operators such as doOnNext, doOnComplete, and doOnError is to create side effect that does not affect the stream. An example of this kind of operations is logging. You should not do any meaningful operation that affect the stream in such operators.

Instead you should be using operators such as map, flatMap, etc.


4.

Putting everything together:

Observable.fromIterable(getDatabaseList())
        .subscribeOn(Schedulers.io())
        .flatMap(database -> transformDatabase(database, DB_1_MAPPER))
        .flatMap(NetworkController::updateRemote)
        .toList() // This has type of Single<List<>>
        .flatMap(list -> {
            // Update db1 and db2 with the result of server update.
            return Single.zip(updateDb1(list), updateDb2(list), (a, b) -> {
                // Combine result of db updates
            });
        })
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(result -> {
            // Handle success case
        }, err -> {
            // Handle error case
        });

Upvotes: 1

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