How to Merge Firestore Queries Locally Using Tasks?

Merging Firestore Queries Locally

As Firestore lacks a logical OR operator, merging multiple queries locally can be a challenge. One approach is to nest queries within the onSuccessListener of another query. However, this can raise concerns about performance.

To address this, an alternative solution using Tasks is recommended. The whenAllSuccess() method merges two or more tasks and invokes a callback when all tasks complete successfully:

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
    }
});

In this example, the list passed to the onSuccess() callback contains the results of both queries in the same order as the tasks were defined.

Another option is the continueWith() method, which chains tasks and invokes a callback when the preceding task completes successfully. The choice between whenAllSuccess() and continueWith() depends on the specific application requirements and use case.

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