What are the ways to merge to Observables / Singles?

Question

I have this code:

public void testGetBlob() throws RequestException {
    TestData.getNewApplication().flatMap(testApplication -> {
        Client.initialize(testApplication.getAppId(), testApplication.getApiToken(), testApplication.getMasterKey());
        assertNotNull(testApplication.getApiToken());
        assertNotNull(testApplication.getAppId());
        assertNotNull(testApplication.getMasterKey());
        Entity entity = new Entity("Todo");
        return entity.create();
    }).flatMap(entity -> entity.setBlobProperty("text", "Hello world!".getBytes("UTF-8")))
            .flatMap(isSuccess -> {
                if(isSuccess) {
                    // need to access `entity` at this point
                    return Single.just(isSuccess);
                } else {
                    return Single.just(false);
                }
            }).subscribe(success -> {
        Browser.getWindow().getConsole().log("Blob created");
        finishTest();
    }, error -> {
        Browser.getWindow().getConsole().error(error.getMessage());
        fail();
    });
    delayTestFinish(5000);
}

In the code above what I need to do is to be able to access the entity object at the point in the comment. How can it be done?

Gustavo Pagani · Accepted Answer · 2019-08-18T07:33:09.000

Between one operator and another you can only emit one object type. In your situation you are emitting a boolean value, but you also want to have access to the Entity object. The solution is to wrap both values (Entity object and boolean value) in a single class and emit that class.

Create a class to wrap the emission of Entity and the result of setBlobProperty.

    class Pair {
        private final Entity entity;
        private final boolean success;

        private Pair(Entity entity, boolean success) {
            this.entity = entity;
            this.success = success;
        }

        public Entity getEntity() {
            return entity;
        }

        public boolean isSuccess() {
            return success;
        }
    }

Then change your code to emit that class:

public void testGetBlob() throws RequestException {
    TestData.getNewApplication().flatMap(testApplication -> {
// ...
        return entity.create();
    }).flatMap(entity -> 
        entity.setBlobProperty("text", "Hello world!".getBytes("UTF-8"))
            // 1. Flat map the setBlobProperty call and emit a Pair with the entity and result
            .flatMap(isSuccess -> Single.just(new Pair(entity, isSuccess)))
    )
            .flatMap(pair -> {
                if(pair.isSuccess()) {
                    // 2. entity is available here via pair.getEntity()
                    return Single.just(isSuccess);
                } else {
                    return Single.just(false);
                }
            }).subscribe(success -> {
// ...
    }
}

Ps: instead of creating your own Pair class, check one of the options from this thread. If you are using Kotlin, there is a Pair class.

What are the ways to merge to Observables / Singles?

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