Firestore get DocumentSnapshot's field's value

Question

If I have a Firebase Firestore database which I have retrieved a DocumentSnapshot for the document corresponding to the collection on the right and stored in a document variable, then how could I retrieve the value in that DocumentSnapshot at the field "username"? The field has a string value.

Answer 1

DocumentSnapshot有一个getString()方法，它接受字段的名称并将其值作为字符串返回。

String value = document.getString("username");

Answer 2

you can use get method to get value of a field

String username = (String) document.get("username");  //if the field is String
Boolean b = (Boolean) document.get("isPublic");       //if the field is Boolean
Integer i = (Integer) document.get("age")             //if the field is Integer

checkout the doc for DocumentSnapshot

Answer 3

You need to do a DocumentReference to get the content in your document.

A simple one will be like this.

DocumentReference docRef = myDB.collection("users").document("username");
docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
@Override
     public void onComplete(@NonNull Task<DocumentSnapshot> task) {
          if (task.isSuccessful()) {
               DocumentSnapshot document = task.getResult();
                    if (document != null) {
                         Log.i("LOGGER","First "+document.getString("first"));
                         Log.i("LOGGER","Last "+document.getString("last"));
                         Log.i("LOGGER","Born "+document.getString("born"));
                    } else {
                         Log.d("LOGGER", "No such document");
                    }
               } else {
                    Log.d("LOGGER", "get failed with ", task.getException());
                }
          }
     });

The downside is that you need to know your document ID to get the field values.

Answer 4

I can only reference the field's data as Strings when I am inside the onComplete, but when I try reference it outside it. I get a nullPointerException and it crashes my activity.

// Gets user document from Firestore as reference
    DocumentReference docRef = mFirestore.collection("users").document(userID);

    docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
        @Override
        public void onComplete(@NonNull Task<DocumentSnapshot> task) {
            if (task.isSuccessful()) {
                DocumentSnapshot document = task.getResult();
                if (document.exists()) {

                    Log.d(TAG, "DocumentSnapshot data: " + document.getData());
                    Log.d(TAG, "db firstName getString() is: " + document.getString("firstName"));
                    Log.d(TAG, "db lastName getString() is: " + document.getString("lastName"));

                    mFirstName = (String) document.getString("firstName");
                    mLastName = (String) document.getString("lastName");
                    Log.d(TAG, "String mFirstName is: " + mFirstName);
                    Log.d(TAG, "String mLastName is: " + mLastName);

                } else {
                    Log.d(TAG, "No such document");
                }
            } else {
                Log.d(TAG, "get failed with ", task.getException());
            }
        }
    });

    //string checking outside the docRef.get().addOnCompleteListener code
    //commented it out because it causes a java.lang.NullPointerException: println needs a message
    //Log.v("NAME", mFirstName);
    //Log.v("NAME", mLastName);

    // sets the text on the TextViews
    tvFirstName = (TextView)findViewById(R.id.tvFirstName);
    tvFirstName.setText(mFirstName);
    tvLastName = (TextView)findViewById(R.id.tvLastName);
    tvLastName.setText(mLastName);

Answer 5

Here is another simple way to get document value(in your case):

Firestore.instance
.collection('users').document('xsajAansjdna')
.get()
.then((value) =>
print("Fetched ==>>>"+value.data["username"]));

Answer 6

`Firestore.instance
.collection('users').document('xsajAansjdna')
.get()
.then((value) =>
print("Fetched ==>>>"+value.data()["username"]));`