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How to read the nested maps from fireStore database from android

In the above image, I have a map that contains an arrays list of 2020, 2021, etc. I want to display the arrays data in RecyclerView. How to do that in android?
Also how to retrieve data if a map contains a list of maps. I'm able to get the documents with field names, but struggling with how to get maps with field names and data in that maps.

DocumentSnapshot's getData() method, returns an object of type Map<String, Object>. Since it's a Map, we can simply get the year and then iterate through the corresponding URLs, like in the following lines of code:
FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
CollectionReference subjectRef = rootRef.collection("subject");
DocumentReference politicalScienceRef = subjectRef.document("political science");
politicalScienceRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
#Override
public void onComplete(#NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()) {
DocumentSnapshot document = task.getResult();
if (document.exists()) {
List<String> urls = new ArrayList<>();
Map<String, Object> data = document.getData();
Map<String, Object> year = (Map<String, Object>) data.get("year");
for (Map.Entry<String, Object> entry : year.entrySet()) {
List<String> yearUrls = (List<String>) entry.getValue();
for (String url : yearUrls) {
urls.add(url);
}
}
for (String url : urls) {
Log.d("TAG", url);
}
} else {
Log.d("TAG", "No such document");
}
} else {
Log.d("TAG", "get failed with ", task.getException());
}
}
});
In the end, simply pass the urls list to an adapter, and display all those URLs into a RecyclerView.

Retrieve an ArrayList from Firebase

I have an ArrayList of Objects in Firebase and I would like to retreive it.
I have 2 array lists. One String and one Grade. When I try to use the array of objects it has a problem:
java.lang.ClassCastException: java.util.HashMap cannot be cast to com.example.gradecalculator.Grade
mDocRef:
private DocumentReference mDocRef = FirebaseFirestore.getInstance().document("myData/Arrays");
Uploading the arrays:
Map<String, Object> dataToSave = new HashMap<String, Object>();
dataToSave.put("StringsArray", stringGrades); // Save Strings Array
dataToSave.put("ObjectsArray", grades); // Save Objects Array
mDocRef.set(dataToSave).addOnSuccessListener(new OnSuccessListener<Void>() {
#Override
public void onSuccess(Void aVoid) {
Log.d(TAG, "Document has been saved!");
Toast.makeText(getApplicationContext(), "List has been saved successfully!", Toast.LENGTH_SHORT).show();
Downloading the arrays:
mDocRef.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
#Override
public void onSuccess(DocumentSnapshot documentSnapshot) {
isListEmpty = false;
if (documentSnapshot.exists()) {
Map<String, Object> dataToLoad = (HashMap<String, Object>) documentSnapshot.getData();
stringGrades = (ArrayList<String>) dataToLoad.get("StringsArray");
grades = (ArrayList<Grade>) dataToLoad.get("ObjectsArray");
for (Grade grade : grades) { // <------------Fails here
System.out.println(grade.toString());
}
First time I'm trying to use Firebase. It seems that it saves the data in the server successfully. Any advice?

The get method of DocumentSnapshot return a List of Map :
List<Map<String, Object>>
You can create another class with your List :
class GradeContainer{
private List<Grade> grades;
public GradeContainer(){}
public List<Grade> getGrades(){
return grades;
}
}
And use dataToLoad.toObject() :
grades = List<Grade> dataToLoad.toObject(GradeContainer.class).getGrades();
You can read this documentation for more informations :
https://firebase.google.com/docs/reference/android/com/google/firebase/firestore/DocumentSnapshot?hl=en
And this tutorial :
https://medium.com/firebase-tips-tricks/how-to-map-an-array-of-objects-from-cloud-firestore-to-a-list-of-objects-122e579eae10

Firebase dealing with nested data

Okay, say I've got the following FireBase database structure.
{
"2143" :
{
"Henk" : 6,
"message" : 1
}
}
With data being added as follows:
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("2143/message");//Testing code, would later be replaced with a session variable and a username variable.
myRef.setValue(1);//Again, mere testing code which sets the 'message' key to have value 1. The actual code is currently lacking as the program isn't entirely functional yet.
I now want to put the players and their respective scores into a leaderboard on an android app in android studio. When I'm trying to put them into a hashmap using the following code:
String code = "2143"; //This is would be the SessionID, it's currently static for testing purposes.
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference(code);
HashMap<String, String> leaderboardMap = new HashMap<>();
...
myRef.orderByValue().addValueEventListener(new ValueEventListener()
{
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot)
{
leaderboardMap.put(dataSnapshot.getKey(), dataSnapshot.getValue().toString());
}
}
I get the following hashmap
key: 2143, value:{Henk=6, message=1}
However I expected the following:
key: Henk, value: 6
key: message, value: 1
Where's the error in my code, and how can I fix it?

You can convert the json string to HashMap and then use those values to display in leaderborad. Here is a function to convert json sring to map.
public static HashMap<String,String> jsonToMap(String t) throws JSONException {
HashMap<String, String> map = new HashMap<String, String>();
JSONObject jObject = new JSONObject(t);
Iterator<?> keys = jObject.keys();
while( keys.hasNext() ){
String key = (String)keys.next();
String value = jObject.getString(key);
map.put(key, value);
}
return map;
}

How to add data to the array of hash map in the document using Firestore?

I want to add data to the existing array without overwriting. And inside each document, I have an array of HashMap. I am trying to add data to the existing one. Kindly check the below code and shed some light.
public void createNewCase(){
Map<String, String> caseInfo = new HashMap<String, String>();
caseInfo.put("chief_complaint", chiefComplaintET.getText().toString());
caseInfo.put("facility", facilityET.getText().toString());
caseInfo.put("location", locationET.getText().toString());
caseInfo.put("assigned_provider", assignProviderET.getText().toString());
caseInfo.put("referring_provider", referringProviderET.getText().toString());
caseInfo.put("admit_date", adminDateET.getText().toString());
caseDictionary.add(caseInfo);
final String patientID = sharedPrefHelper.getStr("patient_id");
db.collection("patients").whereEqualTo("patient_id", patientID).get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
private static final String TAG = "New Case Creation" ;
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
List<HashMap<String,String>> list = new ArrayList<>();
for (QueryDocumentSnapshot document : task.getResult()) {
patient patient = new patient();
list = (List) document.get("patient_case");
for (HashMap<String, String> item:list) {
caseDictionary.add(item);
}
}
System.out.println(caseDictionary);
HashMap<String, Object> uploadData = new HashMap<>();
uploadData.put("patient_case", caseDictionary);
DocumentReference caseRef = db.collection("patients").document(patientID); // am stuck here
}else{
Log.w(TAG, "Error getting documents.", task.getException());
Toast.makeText(NewCase.this, "Something bad happened", Toast.LENGTH_SHORT).show();
Helper.m_Dialog.hide();
}
}
});
}
Edit 1
Below code deleting old data and adding new data. I need to append.
final String patientID = sharedPrefHelper.getStr("patient_id");
final CollectionReference collectionReference = db.collection("patients");
collectionReference.whereEqualTo("patient_id", patientID).get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
Toast.makeText(NewCase.this, task.getResult().toString(), Toast.LENGTH_SHORT).show();
if (task.isSuccessful()) {
for (QueryDocumentSnapshot document : task.getResult()) {
Map<Object, Object> map = new HashMap<>();
map.put("patient_case", caseInfo);
collectionReference.document(document.getId()).set(map, SetOptions.merge());
}
}else{
Toast.makeText(NewCase.this, task.getResult().toString(), Toast.LENGTH_SHORT).show();
}
}
});

As I see in your screenshot, in your patients collection you have documents that contain an array that holds maps (objects). In order to be able to update those maps that exist within your array you should create a Map object that corresponde to your exact document structure and use DocumentReference's set(Object data, SetOptions options) method for that. So pass as the first argument the map and as the second argument SetOptions.merge(). You can find a simpler example in my answer from the following post:
Firestore firebase Android search and update query

This is one of my example
i have done it like this
List<Map> history = List();
History historyObj = History(typee, name, timeStamp, pointsBefore, points, itemPoints);
history.add(historyObj.toMap());
//Firesore collection object
CollectionReference child = _firestore.collection('children');
//Firesore document object
DocumentReference docRef = child.doc(selectedChild.childId);
// "history" is your "patient_case"
docRef.update({"history": FieldValue.arrayUnion(history)}).then(
(value) => print("Update done"));
History is one of my class
History class includes method toMap() which converts all history class variables and its values to 'Key' : 'value' form like this
Map<String, dynamic> toMap() => {
"type": type,
"name": name,
"timestamp": timestamp,
"points_before": points_before,
"points_after": points_after,
"points_affected": points_affected,
};

Posted data missing using firebase

I'm trying to insert some data into my firebase but encountered the following error, the 2nd data is missing. Here are the code:
Firebase.setAndroidContext(this);
Button btnSave = (Button) findViewById(R.id.btnSave);
btnSave.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
try {
//Creating firebase object
Firebase ref = new Firebase(Config.FIREBASE_URL);
//Getting values to store
String name = mName.getText().toString().trim();
String address = mAddress.getText().toString().trim();
String latlng = mLatLng.getText().toString().trim();
//Creating Person object
FM_Spots spots = new FM_Spots();
//Adding values
spots.setName(name);
spots.setAddress(address);
spots.setLatLng(latlng);
//Storing values to firebase
//ref.child("FM_Spots").setValue(spots);
Firebase newRef = ref.child("FM_Spots").push();
newRef.setValue(spots);
} catch (Exception e) {
Toast.makeText(getApplicationContext(), e.getMessage().toString(), Toast.LENGTH_SHORT).show();
}
}
});
}
I only have 2 fields which are name and the address is having data from the last field (latlng). Please advise, thank you.
-sea-

When you said "2nd data" you meant that the second field of the writable object is missing, right?
If so, you can use updateChildren(Map map) method instead of setValue() to specify fields you want to write directly:
newRef.updateChildren(convertFMSpotsToMap(spots));
where convertFMSpotsToMap() is something like this:
private static Map<String, Object> convertFMSpotsToMap(#NonNull FM_Spots spots) {
HashMap<String, Object> map = new HashMap<>();
map.put("name", spots.getName());
map.put("address", spots.getAddress());
return map;
}