I want to read data from my Firebase database for all questions. For e.g. for question1 I want to store ques,ans and answeredBy into three variables. What I am currently doing is here.
private FirebaseDatabase database=FirebaseDatabase.getInstance();
private DatabaseReference
quizRef=database.getReference("Quiz").child("Questions");
quizRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot ds:dataSnapshot.getChildren())
{
ModelClass modelClass=new ModelClass();
modelClass.setQues(ds.child("question1").getValue(ModelClass.class).getQues());
modelClass.setAns(ds.child("question1").getValue(ModelClass.class).getAns());
textViewQuestionText.setText(modelClass.getQues());
}
}
#Override
public void onCancelled(DatabaseError error) {
textViewQuestionText.setText("Error occurred");
}
});
Tried and Tested. You dont have to check for keys like question1,question2 etc
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference reference = database.getReference("Quiz/Questions");
reference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot ds: dataSnapshot.getChildren()) {
ModelClass modelClass = (ds.getValue(ModelClass.class));
modelClass.getAns();
modelClass.getQes();
// fetch any key value pair
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
I recommend to use firebase generated hash keys instead of your own keys like question1,question2 etc
Check this
You can just use the data from your Firebase Database directly using the following code:
DatabaseReference q1Ref = quizRef.child("question1");
q1Ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String question = dataSnapshot.child("ques").getValue(String.class);
String answer = dataSnapshot.child("ans").getValue(String.class);
int ansBy = dataSnapshot.child("answeredBy").getValue(Integer.class);
// now you can do what you want with the values stored in the variables
}
#Override
public void onCancelled(DatabaseError error) {
textViewQuestionText.setText("Error occurred");
}
});
To read or write data from the database, you need an instance of DatabaseReference:
private DatabaseReference mDatabase;
// ...
mDatabase = FirebaseDatabase.getInstance().getReference();
To read data at a path and listen for changes, use the addValueEventListener() or addListenerForSingleValueEvent() method to add a ValueEventListener to a DatabaseReference.
You can use the onDataChange() method to read a static snapshot of the contents at a given path, as they existed at the time of the event.
For more information you can refer to firebase docs
Related
I'am trying to store the query result in a String variable, but the result I'm getting is the string conversion of the query object.
tableDatabaseReference = FirebaseDatabase.getInstance().getReference("tables");
tableNameQuery = tableDatabaseReference.child("tableName").orderByChild(tableID).equalTo("123");
String tableName = tableNameQuery.toString();
Any suggestions?
EDIT:
Database structure:
Tables:
-------TableID:
--------------TableName:
--------------TableID:
To retrieve data from Firebase Realtime database , you have to add a valueEventListener to your database reference variable like this
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference dataRef = database.getReference("YOUR_DATABASE_REF");
dataRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
// here you can get your data from this snapshot object
String data = dataSnapshot.getValue("CHILD_NAME_HERE").toString();
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
To get data once you can use singleValueEventListener
dataRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
// here you can get your data from this snapshot object
String data = dataSnapshot.getValue("CHILD_NAME_HERE").toString();
}
#Override
public void onCancelled(DatabaseError databaseError) {}
});
Firebase operation is asynchronous, so you have to wait to complete the operation to get result. To access data outside of onDataChange you can use LiveData and observe it outside. When you get data inside onDataChange then notify LiveData by posting value. Check below:
private MutableLiveData<String> tableName = new MutableLiveData<>();
DatabaseReference tableDatabaseReference = FirebaseDatabase.getInstance().getReference("tables");
tableDatabaseReference
.child(tableID)
.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
String data = dataSnapshot.child("tableName").getValue(String.class);
//Now post that value to LiveData
tableName.postValue(data);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
Observe data here
tableName.observe(this, name -> {
// use name here
});
I am writing to the realtime database in a method using
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("Test");
myRef.setValue("test");
Database structure
Later on I am trying to retrieve this string in another method using
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("Test");
ValueEventListener valueEventListener = myRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
value = dataSnapshot.getValue(String.class);
}
#Override
public void onCancelled(DatabaseError error) {
}
});
I want value to read "test" but it always returning null.
Use this technique to resolve your issue
mRef=FirebaseDatabase.getInstance().getReference().child("Test")
ValueEventListener listener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
// Get Post object and use the values to update the UI
value = dataSnapshot.getValue(String.class);
Log.d("yourtag ", " Result= "value);
// ...
}
#Override
public void onCancelled(DatabaseError databaseError) {
// Getting Post failed, log a message
Log.w(TAG, "loadPost:onCancelled", databaseError.toException());
// ...
}
};
mRef.addValueEventListener(listener);
I need a help in firebase database,
I am willing to create an app for a city like Kolkata, to find buses between different local stations, I want to save the data in database and user will input where to where they want to go, after clicking on search, list of available data will be shown,
But I need help in how should I save the data to fetch it easily with less complicated code.
You can save data easily with firebase
private void writeNewUser(String userId, String name, String email) {
User user = new User(name, email);
mDatabase.child("users").child(userId).setValue(user);
}
You can search from firebase like below
DatabaseReference mFirebaseDatabaseReference = FirebaseDatabase.getInstance().getReference();
Query query = mFirebaseDatabaseReference.child("users").orderByChild("name").equalTo("Fazal");
query.addValueEventListener(valueEventListener);
ValueEventListener valueEventListener = new ValueEventListener()
{
#Override
public void onDataChange(DataSnapshot dataSnapshot)
{
for (DataSnapshot postSnapshot : dataSnapshot.getChildren())
{
//TODO get the data here
User user = dataSnapshot.getValue(User.class);
}
}
#Override
public void onCancelled(DatabaseError databaseError)
{
}
};
EDIT:
Firebase dont have a great SQL like searches built in. You can either sort by values/key or you can equalto
https://firebase.google.com/docs/database/android/retrieve-data
for further details check fire-base documentation
https://firebase.google.com/docs/database/android/read-and-write
when you write data into firebase database used below code ..
make pojo class for insert data..
public class City {
public String name, code;
public City(String name, String code) {
this.name = name;
this.code = code;
}
}
then after when you insert data into firebase used below code..
private DatabaseReference mFirebaseDatabase;
private FirebaseDatabase mFirebaseInstance;
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.register_layout);
mFirebaseDatabase = mFirebaseInstance.getReference("usersDb/UserTable");//define your database name and table name
}
// below method used insert data..
private void insertData(){
City city=new City("Ahmedabad","380016"); // you can add data also runtime.
mFirebaseDatabase.child(city.name).setValue(user);
}
// below method used to search data..
private void sqlQuery(){
DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
Query query = reference.child("usersDb").child("UserTable").orderByChild("name").equalTo("vikas#gmail.com");
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
for (DataSnapshot issue : dataSnapshot.getChildren()) {
Log.d("Value::",issue.getValue(User.class).email);
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
I want to access article information but the problem I face is Article array names are some random keys and not like the one given here.
To access the keys inside the Article node, do the following:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = rootRef.child("Branch").child("Users");
ref.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot datas: dataSnapshot.getChildren()){
String key=datas.child("keys").getValue().toString();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Here the datasnapshot is Users you then iterate inside the random keys and get the values(keys) that are inside the Articles.
I want to get the value of 'caste' key from the JSON tree in Firebase Realtime Database.See this image
I have the user's unique ID and all my auth and user objects are in place. How do I get a reference to only the 'caste' key into a String variable?
Thanks,
DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference("project-android-536f3");
mDatabase.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot messageSnapshot : dataSnapshot.getChildren()) {
String caste = (String) messageSnapshot.child("caste").getValue();
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
I figured it out. I never provided the unique User ID so it never got data from the database.
final FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference ref = database.getReference(firebaseUser.getUid()).child("caste");
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
caste = dataSnapshot.getValue().toString();
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});