How to query a list of strings instead of a single string and get a list of results from Firestore [duplicate]

Question

I have a list of IDs of favorite items of a user locally stored in a list of strings. Now when user opens his favorite section the app needs to fetch all the items in the local favorite list from Cloud Firestore. Now what I see is only query that accepts a field and only a string (in my case only a single id of favorite item at a time).

Is there a way to pass the list of IDs as a Query in a single operation and get the result. What I am doing now is passing the IDs to RecylerView adapter and fetching it one by one in the BindViewHolder.

@Override
public void onBindViewHolder(final ImageViewHolder holder, int position) {

    db.whereEqualTo("imageId",mUploads.get(position))
            .get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
        @Override
        public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
            List<Upload> uploadsList = queryDocumentSnapshots.toObjects(Upload.class);
            Upload uploadCurrent = uploadsList.get(0);

            holder.materialCardView.setCardBackgroundColor(Color.parseColor(uploadCurrent.getImageColor()));
            Glide.with(mContext)
                    .load(uploadCurrent.getImageUrl())
                    .transition(DrawableTransitionOptions.withCrossFade())
                    .centerCrop()
                    .into(holder.imageView);

        }
    });

}

i don't believe there is. I'm pretty sure you'd have to do a for loop and pass the data to your adapter and notify it or just continue doing what you're doing. — LinuxMasterRace
– LinuxMasterRace, Commented Jul 11, 2019 at 12:26
Repeating the data fetch every time in the adapter is a little overhead right? — Frisky Coder
– Frisky Coder, Commented Jul 11, 2019 at 12:30

Alex Mamo · Accepted Answer · 2019-07-11 13:22:18Z

2

Is there a way to pass the list of IDs as a Query in a single operation and get the result.

No, there is not not. You cannot pass a list or an array of strings to your query and get the results in one go. When calling get() on a Query object, the object that is returned is of type Task. Iterate through your list, create those Task objects and add all of them to a List<Task<DocumentSnapshot>> and then pass that list to Tasks's whenAllSuccess() method as it is explained in my answer from the following post:

Android Firestore convert array of document references to List<Pojo>

Edit:

You should iterate through your list of strings and create the Task objects.

Task<DocumentSnapshot> documentSnapshotTask = collRef.document(stringFromList).get();

So at every iteration add the Task object to a list of tasks:

List<Task<DocumentSnapshot>> tasks = new ArrayList<>();

At the end just pass tasks list to whenAllSuccess() method, that's it.

edited Jul 11, 2019 at 13:22

answered Jul 11, 2019 at 12:29

Alex Mamo

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4 Comments

Frisky Coder Over a year ago

Sorry but I didn't quite understood that.The list of my IDs in List<String> and I need to get result list as of the form List<Uploads>. My collections name is "uploads" and the field of document that should be matched to is "imageId"

Alex Mamo Over a year ago

Check also the duplicate, it's the exact same thing, right?

Frisky Coder Over a year ago

But we should pass a field and its corresponding value as query in that case right?

Alex Mamo Over a year ago

Please see my updated answer and tell me if it works.

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