Firestore Array of Document References

Question

I have the following structure of my Firestore database:

products:{ // Collection
    procuct_1: { // Document
       title:"",
       url:""

videos:{ // Collection
    video_1:{ // Document
       title:"",
       products:{ // Array of references 
            0: "/products/product_1,
            1: "/products/product_2

I would like to be able from Array field in Videos Collection to get Document References to Products collection in order to get values of some fields of this collection (ex. title of product).

For the moment I use this code:

    FirebaseFirestore firebaseFirestore = FirebaseFirestore.getInstance();
    firebaseFirestore
            .collection("videos")
            .get()
            .addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
                @Override
                public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                    if (task.isSuccessful()) {
                        DocumentSnapshot documentSnapshot = task.getResult();

                        Map<String, Object> map = documentSnapshot.getData();
                        for (Map.Entry<String, Object> entry: map.entrySet()){
                            if (entry.getKey().equals("products")){
                               textView.setText(entry.getValue().toString());
                            }
                        }

But entry.getValue().toString(), returns me such array:

[com.google.firebase.firestore.DocumentReference@451d5ae8,

com.google.firebase.firestore.DocumentReference@e28cd0c]

Any suggestions how I can get any field of Product collection from this Array?

Alex Mamo · Accepted Answer · 2018-03-28 11:51:30Z

1

To solve this, please use the following code:

firebaseFirestore.collection("videos")
    .get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {
            for (DocumentSnapshot document : task.getResult()) {
                List<String> products = (List<String>) document.get("products");
                for (String product : products) {
                    Log.d("TAG", product);
                }
            }
        }
    });

The output will be:

/products/product_1
/products/product_2

edited Mar 28, 2018 at 11:51

answered Mar 26, 2018 at 13:51

Alex Mamo

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2 Comments

Kiwi Over a year ago

Thanks for your answer. But I am getting an error java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.util.Map on this line of code Map<String, Object> products = (Map<String, Object>) document.get("products");

Alex Mamo Over a year ago

Sorry for my late answer. I didn't see the brackets in your database structure so I thought it is a Map and that's why that error. Please see my updated answer. It works for sure now.

Kiwi · Accepted Answer · 2018-03-28 09:47:37Z

1

This code allowed me to reach the result that I needed

FirebaseFirestore firebaseFirestore = FirebaseFirestore.getInstance();
    firebaseFirestore
            .collection("videos")
            .get()
            .addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
                @Override
                public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                    DocumentSnapshot document = task.getResult();
                    ArrayList<DocumentReference> products = (ArrayList<DocumentReference>) document.get("products");
                    for (int i = 0; i < products.size(); i++) {
                        DocumentReference ref = products.get(i);
                        ref.get()
                                .addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
                                    @Override
                                    public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                                        if (task.isSuccessful()) {
                                            DocumentSnapshot document = task.getResult();
                                            if (document != null && document.exists()) {
                                                BestBuysProducts best_buy = document.toObject(BestBuysProducts.class);
                                                Log.d(TAG, "Title: " + best_buy.getProduct_title());
                                            }
                                        }
                                    }
                                });
                    }
                }
            });

answered Mar 28, 2018 at 9:47

Kiwi

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2 Comments

Alex Mamo Over a year ago

I see that is working but what you are doing is not a good practice because you are attaching a listener for every iteration of that loop. So keeping listeners for data you don't need to keep it synchronized is wasteful. Please see my updated answer using only a few lines of code.

Alex Mamo Over a year ago

Good to hear that it worked! If you think that my answer helped you, please consider accepting it. Thanks!

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