How Can I Combine Firestore Queries Locally Using Tasks.whenAllSuccess()?

Merging Firestore Queries Locally

When working with Firestore, there is no logical OR operator to combine queries. To merge two separate queries locally, you can utilize the Tasks.whenAllSuccess() method.

Tasks.whenAllSuccess() takes a list of tasks as arguments and returns a new task that completes successfully only when all the input tasks complete successfully. The result of the returned task is a list of the results of the input tasks, in the same order in which the input tasks were passed.

Here's how you can merge two queries using Tasks.whenAllSuccess():

FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
Query firstQuery = rootRef...
Query secondQuery = rootRef...

Task firstTask = firstQuery.get();
Task secondTask = secondQuery.get();

Task combinedTask = Tasks.whenAllSuccess(firstTask, secondTask).addOnSuccessListener(new OnSuccessListener<List<Object>>() {
    @Override
    public void onSuccess(List<Object> list) {
        // Do what you need to do with your list
    }
});

When you override the onSuccess() method of the combined task, you'll receive a list of objects with the exact order of the tasks that were passed as arguments into the whenAllSuccess() method. This allows you to merge the results of the two queries while maintaining their proper order.

Instead of Tasks.whenAllSuccess(), you can also consider using Tasks.continueWith() to achieve a similar result. However, the choice between the two methods depends on the specific use case of your application. Refer to the official documentation for more details on Tasks.continueWith().

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