How to get data from a map field from Firebase Firestore?-CodePudding

I want to retrieve data stored as a map field on Cloud Firestore.
I want to get the 'Comment' as a string from 'All Comments' field to show it in a TextView.

How can I do it? (Java)

I tried this to add the data

                Map<String,String> allComments=new HashMap<String,String>();
                String commentContent=commentboxedittext.getText().toString();
                allComments.put("Movie Name",name);
                allComments.put("Comment",commentContent);
                firebaseFirestore.collection("All Comments").document("MovieComments").set(allComments, SetOptions.merge());

And this to retrieve the data

DocumentReference docRef = firebaseFirestore.collection("All Comments").document("MovieComments");
                docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                        if (task.isSuccessful()) {
                            DocumentSnapshot document = task.getResult();
                            if (document.exists()) {
                                Map<String, Object> m=document.getData();
                                userComment=m.get("Comment").toString();
                                mName=m.get("Movie Name").toString();
                            } else {
                                Toast.makeText(MovieDetails.this, "No Such Document", Toast.LENGTH_SHORT).show();
                            }
                        } else {
                            Toast.makeText(MovieDetails.this, "Error", Toast.LENGTH_SHORT).show();
                        }
                    }
                });

But app crashes on doing this.
I also tried doing this to put the data and it worked but then I do not know how to retrieve data form this method.

            Map<String,String> allComments=new HashMap<String,String>();
            Map<String, Object> user=new HashMap<String,Object>();
        userID=firebaseAuth.getCurrentUser().getUid();
        userReference=firebaseFirestore.collection("Users ").document(userID);
            String commentContent=commentboxedittext.getText().toString();
            allComments.put("Movie Name",name);
            allComments.put("Comment",commentContent);
            user.put("All Comments",allComments);
            userReference.set(user, SetOptions.merge()).addOnSuccessListener(new OnSuccessListener<Void>() {
                @Override
                public void onSuccess(Void unused) {
                    Toast.makeText(MovieDetails.this, "Comment Added", Toast.LENGTH_SHORT).show();
                }
            }).addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {
                    if(e instanceof FirebaseNetworkException)
                        Toast.makeText(MovieDetails.this, "No Internet Connection", Toast.LENGTH_SHORT).show();
                    Toast.makeText(MovieDetails.this, "Values Not Stored", Toast.LENGTH_SHORT).show();
                }
            });

CodePudding user response：

Assuming that "l4ir...Xy12" is ID of the authenticated user, to get the value of the "Comment" that exists within the "All Comments" map, please use the following lines of code:

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
FirebaseFirestore db = FirebaseFirestore.getInstance();
db.collection("users").document(uid).get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
    @Override
    public void onComplete(@NonNull Task<DocumentSnapshot> task) {
        if (task.isSuccessful()) {
            DocumentSnapshot document = task.getResult();
            if (document.exists()) {
                String comment = ((HashMap<String, Object>) document.getData().get("All Comments")).get("Comment").toString();
                Log.d("TAG", comment);
            } else {
                Log.d("TAG", "No such document");
            }
        } else {
            Log.d("TAG", "get failed with ", task.getException());
        }
    }
});

The result in the logcat will be:

sfgs

A few things to note:

DocumentSnapshot#get(String field) returns an object of type Object. Since each field inside a document represents a pair of keys and values, we can cast the result to an object of type HashMap<String, Object>.
Since we already have a Map, we can get the call Map#get(Object key) method, which returns the value associated with the key.