如何在 Firestore 中将文档分组？

Question

I have an ArrayList<String> ids which I can use to get documents inside a collection. For each ID in the array list of ids, I can do:

 DocumentReference doc = fstore.collection("Collection").document(id);

For a normal query you'd use:

 Query query = fstore.collection("Collection").whereEqualTo("field", value).orderBy("Field", Query.Direction.DESCENDING).limit(5);

And then you can use get() to get the documents.

My question is how do I group these documents together so I can perform operations like limit orderBy and other methods available for collection queries.

Answer 1

The simplest solution I can think of would be to save each operation you perform into a Task object and add each object to a List. As soon as the iteration completes, pass that list to Tasks#whenAllSuccess(Collection> tasks) method, as you can see in the following lines of code:

List<Task<DocumentSnapshot>> tasks = new ArrayList<>();
for (String id : ids) {
    Task<DocumentSnapshot> task = db.collection("Collection").document(id).get();
    tasks.add(task);
}
Tasks.whenAllSuccess(tasks).addOnSuccessListener(new OnSuccessListener<List<Object>>() {
    @Override
    public void onSuccess(List<Object> list) {
        //Do what you need to do with your list
        for (Object object : list) {
            ModelClass mc = ((DocumentSnapshot) object).toObject(ModelClass.class);
        }
    }
});