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firestore query in for loop android java

I am new to java. I have a firestore_member_list. In firestore_member_list, it contains values: ["steve","ram","kam"]. I am using for loop to pass values one by one.
loadingbar.show()
for( int k=0; k<firestore_member_list.size();k++){
String member_name = firestore_member_list.get(k);
final DocumentReference memDataNameCol = firestoredb.collection("member_collection").document(member_name);
memDataNameCol.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
#Override
public void onComplete(#NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()) {
DocumentSnapshot document = task.getResult();
if (document.exists()) {
// In here, I am retreiveing the document data from firestore and assigning it to the ArrayList which is `all_mem_data`
all_mem_data.add(document.get("member_name").toString());
all_mem_data.add(document.get("member_address").toString());
Toast.makeText(getActivity(), "all mem data array"+all_mem_data.toString(),
Toast.LENGTH_LONG).show();
}
}
}
});
}
Log.d("all_mem_data",all_mem_data)
loadingbar.hide()
I know firestore executes asynchronously. Since firestore retrieves data asynchronous, before filling the array of all_mem_data, the last line gets executed and shows the empty array. How to wait for the array to get filled and after filling,execute the last two lines. Please help me with solutions.

Any code that needs the data from the database, needs to be inside the onComplete that fires when that data is available.
If you want to wait until all documents are loaded, you can for example keep a counter:
loadingbar.show()
int completeCount = 0;
for( int k=0; k<firestore_member_list.size();k++){
String member_name = firestore_member_list.get(k);
final DocumentReference memDataNameCol = firestoredb.collection("member_collection").document(member_name);
memDataNameCol.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
#Override
public void onComplete(#NonNull Task<DocumentSnapshot> task) {
...
if (completeCount++ == firestore_member_list.size()-1) {
Log.d("all_mem_data",all_mem_data)
loadingbar.hide()
}
}
});
}

Wait until Firestore data is retrieved

I need after inner foreach finish and add all data in list then send to interface
but when but this line " view.setOrders(orderList); " below " orderList.add(order); "
my code run okye but not that is not performance , I need best way to collection list then send to interface ..
public ListenerRegistration getOrders() {
view.showLoading();
ListenerRegistration listenerRegistration = refOrders.addSnapshotListener((queryDocumentSnapshots, e) -> {
view.hideLoading();
if (e != null) {
view.onErrorMessage(e.getMessage());
} else {
List<Order> orderList = new ArrayList<>();
for (QueryDocumentSnapshot snapshot : queryDocumentSnapshots) {
Order order = snapshot.toObject(Order.class);
order.setOrderId(snapshot.getId());
refUsers.document(order.getPhone()).get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
#Override
public void onComplete(#NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()) {
User user = task.getResult().toObject(User.class);
order.setName(user.getName());
order.setAddress(user.getAddress());
orderList.add(order);
}
}
});
}
//Here Back List size = 0
view.setOrders(orderList);
}
});
return listenerRegistration;
}

Since get() method is asynchronous which means that the code after the CompletionListener will be executed first and then after the data is retrieved the listener will get executed.
Therefore to solve the issue add the following line view.setOrders(orderList); inside the CompletionListener
if (task.isSuccessful()) {
User user = task.getResult().toObject(User.class);
order.setName(user.getName());
order.setAddress(user.getAddress());
orderList.add(order);
view.setOrders(orderList);

Firestore not querying second collection

I'm kind of new to android studio and firestore database and
I'm having some trouble with querying my second firestore collection. As the title says, i am querying two collections, first one is:
with the code :
firestore = FirebaseFirestore.getInstance();
FirebaseFirestoreSettings settings = new FirebaseFirestoreSettings.Builder()
.build();
firestore.setFirestoreSettings(settings);
firestore.collection("Obiective").get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
//<--------- Check if firestore entry is already downloaded into file --------->
SingletonObjectivesId.getInstance().getIds().clear();
for (QueryDocumentSnapshot document : task.getResult()) {
Log.d(TAG, task.getResult().size() + " number of documents");
SingletonObjectivesId.getInstance().setSize(task.getResult().size());
if(document.exists() && document != null) { ...
and the second collection have the following format:
with the code:
firestore.collection("Routes")
.get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
Log.d(TAG, task.getResult().size() + " = task.getResult().size()");
for (QueryDocumentSnapshot document : task.getResult()) {
objectives_id.clear();
id_route = document.getId();
if(document.exists() && document != null) {
Map<String, Object> map = document.getData();
for (Map.Entry<String, Object> entry : map.entrySet()) {
String field_name = entry.getKey() + "";
String id = document.getString(field_name) + "";
objectives_id.add(id);
}
}
routes.add(new Route(objectives, objectives_id, id_route));
}
} else {
Log.d(TAG, "Error getting documents: ", task.getException());
}
}
});
As you can see in the second code i added a Log.d ( after if (task.isSuccessful()) ) who will display the number of documents. In my case, the first query Log.d returns 3 and the second returns 0 despite the fact that i have 2 documents in there. How can i access this 2 documents ?
Thank you.

Firebase APIs are asynchronous, meaning that the onComplete() method returns immediately after it's invoked, and the callback from the Task it returns, will be called some time later. There are no guarantees about how long it will take. So it may take from a few hundred milliseconds to a few seconds before that data is available. Because that method returns immediately, the number of documents that you try to log, is not populated from the callback yet.
Basically, you're trying to use a value synchronously from an API that's asynchronous. That's not a good idea. You should handle the APIs asynchronously as intended.
A quick solve for this problem would be to move the code that queries the second collection inside the first callback (inside the onComplete() method) so-called nested queries, otherwise I recommend you see the last part of my anwser from this post in which I have explained how it can be done using a custom callback. You can also take a look at this video for a better understanding.

After i followed the steps from the video, i updated the code like this:
I have a global variable firestore created at the beginning of my class
private FirebaseFirestore firestore;
I have two methods readDataObjective and readDataRoute and two interfaces FirestoreCallback and FirestoreCallbackRoutes
readDataRoutes
private void readDataRoute(FirestoreCallbackRoute firestoreCallbackRoute){
firestore.collection("Trasee").get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
for (QueryDocumentSnapshot document : task.getResult()) { ...
readDataObjective
private void readDataObjective(FirestoreCallback firestoreCallback){
firestore.collection("Obiective").get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
SingletonObjectivesId.getInstance().getIds().clear();
for (QueryDocumentSnapshot document : task.getResult()) { ...
Interfaces
private interface FirestoreCallback{
void onCallback(ArrayList<Objective> list);
}
private interface FirestoreCallbackRoute{
void onCallback(ArrayList<Route> list);
}
And in onCreate method i call readDataObjective and readDataRoute like this
firestore = FirebaseFirestore.getInstance();
FirebaseFirestoreSettings settings = new FirebaseFirestoreSettings.Builder().build();
firestore.setFirestoreSettings(settings);
readDataObjective(new FirestoreCallback() {
#Override
public void onCallback(ArrayList<Objective> list) {
for(Objective item : list){
//Create plainText Object - delimiter "/~/"
String data = "Title:" + item.getTitle() + "/~/" +
............................
} else if(str.contains("Longitude:")){
obj.setLongitude(str.substring(10,str.length()));
}
start = crt + 2;
}
}
SingletonObjectivesArray.getInstance().getObjectives().add(obj);
}
readDataRoute(new FirestoreCallbackRoute() {
#Override
public void onCallback(ArrayList<Route> list) {
Log.d(TAG, 2 + " ");
ArrayList<Objective> routeObjectives = new ArrayList<>();
for (int i = 0; i < list.size(); i++) {
routeObjectives.clear();
for (int j = 0; j < SingletonObjectivesArray.getInstance().getObjectives().size(); j++){ ...
With the mention that readDataRoute is called inside readDataObjective, at the end of it.
I noticed that the problem is not only with the second query, but with the first one too. I added a new document into the first collection and after running the code, the first query return the old data ( without my new entry ).

How to get a list of Strings from inside of a document Firestore

I have stored a list of Strings inside a document.i have given it a name("name") now i am trying to get it on the client side but do not know how to do it exactly. i can see that if my field is of type number i can use getLong("Fieldname") but i am unable to figure it out how to get back a list of type Strings.
My code so far
FirebaseFirestore getlistofbrands=FirebaseFirestore.getInstance();
getlistofbrands.collection(FireStoreConstants.COL_BRANDNAMESONLY).document("Brands").get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
#Override
public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
List<String> listofbrandsfromfirestore=queryDocumentSnapshots.getDocuments().toArray(String.class);
also tried this
List<String> listofbrandsfromfirestore=queryDocumentSnapshots.toObjects(String.class);
how i uploaded the data
Map < String, Object > docData = new HashMap < > ();
List < String > deviceNameList = new ArrayList < String > ();
deviceNameList.add("brand1");
deviceNameList.add("brand2");
deviceNameList.add("brand3");
deviceNameList.add("brand4");
docData.put("name", deviceNameList);
firebaseFirestore.collection("FireStoreConstants.COL_BRANDNAMESONLY")
.document("Brands").set(docData).addOnSuccessListener(new
OnSuccessListener < Void > () {
#Override
public void onSuccess(Void aVoid) {
Log.d(TAG, "Repository:onSuccess:");
}
}).addOnFailureListener(new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
Log.d(TAG, "Repository:error" + e.toString());
}
});

Since you store the brand names in a single document, I doubt QuerySnapshot is the right class to get back. As far as I can see, you'll want to use getData() to get the Map<String, Object> that Firestore uses for your List:
getlistofbrands
.collection(FireStoreConstants.COL_BRANDNAMESONLY)
.document("Brands")
.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());
Map<String, String> brandsMap = (Map<String, String>)documen.getData().getData("AllBrands");
List<String> brands = new LinkedList<String>();
for (String key: brandsMap.keySet()) {
brands.add(brandsMap.get(key));
}
// TODO: use the brands list
} else {
Log.d(TAG, "No such document");
}
} else {
Log.d(TAG, "get failed with ", task.getException());
}
}
});
You might also want to try:
List<String> brands = brandsMap.value();

i used the code provided by #Frank van and used this function to cast my Object to a list of Strings
#SuppressWarnings("unchecked")
public static <T extends List<?>> T cast(Object obj) {
return (T) obj;
}
Object brandsobj = queryDocumentSnapshots.getData().get("AllBrands");
List<String> allbrands = cast(brandsobj);

You can check out this question post I had posted earlier. You can change from the ArrayAdapter that I have used to a List
AutoCompleteTextView data from Firestore
Hope it helps you.

Add new field or change the structure on all Firestore documents

Consider a collection of users. Each document in the collection has name and email as fields.
{
"users": {
"uid1": {
"name": "Alex Saveau",
"email": "saveau.alexandre#gmail.com"
},
"uid2": { ... },
"uid3": { ... }
}
}
Consider now that with this working Cloud Firestore database structure I launch my first version of a mobile application. Then, at some point I realize I want to include another field such as last_login.
In the code, reading all the users documents from the Firestore DB using Java would be done as
FirebaseFirestore.getInstance().collection("users").get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
for (DocumentSnapshot document : task.getResult()) {
mUsers.add(document.toObject(User.class));
}
}
}
});
where the class User contains now name, email and last_login.
Since the new User field (last_login) is not included in the old users stored in the DB, the application is crashing because the new User class is expecting a last_login field which is returned as null by the get() method.
What would be the best practice to include last_login in all the existing User documents of the DB without losing their data on a new version of the app? Should I run an snippet just once to do this task or are there any better approaches to the problem?

You fell into a gap of NOSQL databases: Document oriented databases do not guarantee structural integrity of the data (as RDBMS do)
The deal is:
in an RDBMS all stored data have the same structure at any given time (within the same instance or cluster). When changing the structure (ER-diagram) you have to migrate the data for all existing records which costs time and effort.
As a result, your application can be optimized for the current version of the data structure.
in a Document oriented database each record is an independent "Page" with its own independent structure. If you change the structure it only applies to new documents. So you don't need to migrate the existing data.
As a result, your application must be able to deal with all versions of the data structure you've ever used in your current database.
I don't know about firebase in detail but in general you never update a document in a NOSQL database. You only create a new version of the document. So even if you update all documents your application must be prepared to deal with the "old" data structure...

I wrote some routines to help automate this process back when I posted the question. I did not post them since these are a bit rudimentary and I was hoping for an elegant Firestore-based solution. Because such solution is not still available, here are the functions I wrote.
In short, we have functions for renaming a field, adding a field, or deleting a field. To rename a field, different functions are used depending on the data type. Maybe someone could generalise this better? The functions below are:
add_field: Adds a field in all documents of a collection.
delete_field: Deletes a field in all documents of a collection.
rename_*_field: Renames a field containing a certain data type (*) in all documents of a collection. Here I include examples for String, Integer, and Date.
Add field:
public void add_field (final String key, final Object value, final String collection_ref) {
FirebaseFirestore.getInstance().collection(collection_ref).get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
WriteBatch batch = db.batch();
for (DocumentSnapshot document : task.getResult()) {
DocumentReference docRef = document.getReference();
Map<String, Object> new_map = new HashMap<>();
new_map.put(key, value);
batch.update(docRef, new_map);
}
batch.commit();
} else {
// ... "Error adding field -> " + task.getException()
}
}
})
.addOnFailureListener(new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
// ... "Failure getting documents -> " + e
}
});
}
Delete field:
public void delete_field (final String key, final String collection_ref) {
FirebaseFirestore.getInstance().collection(collection_ref).get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
WriteBatch batch = db.batch();
for (DocumentSnapshot document : task.getResult()) {
DocumentReference docRef = document.getReference();
Map<String, Object> delete_field = new HashMap<>();
delete_field.put(key, FieldValue.delete());
batch.update(docRef, delete_field);
}
// Commit the batch
batch.commit().addOnCompleteListener(new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
// ...
}
});
} else {
// ... "Error updating field -> " + task.getException()
}
}
})
.addOnFailureListener(new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
// ... "Failure getting notices -> " + e
}
});
}
Rename field:
public void rename_string_field (final String old_key, final String new_key, final String collection_ref) {
FirebaseFirestore.getInstance().collection(collection_ref).get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
WriteBatch batch = db.batch();
for (DocumentSnapshot document : task.getResult()) {
DocumentReference docRef = document.getReference();
String old_value = document.getString(old_key);
if (old_value != null) {
Map<String, Object> new_map = new HashMap<>();
new_map.put(new_key, old_value);
Map<String, Object> delete_old = new HashMap<>();
delete_old.put(old_key, FieldValue.delete());
batch.update(docRef, new_map);
batch.update(docRef, delete_old);
}
}
// Commit the batch
batch.commit().addOnCompleteListener(new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
// ...
}
});
} else {
// ... "Error updating field -> " + task.getException()
}
}
})
.addOnFailureListener(new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
// ... "Failure getting notices ->" + e
}
});
}
public void rename_integer_field (final String old_key, final String new_key, final String collection_ref) {
FirebaseFirestore.getInstance().collection(collection_ref).get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
WriteBatch batch = db.batch();
for (DocumentSnapshot document : task.getResult()) {
DocumentReference docRef = document.getReference();
int old_value = document.getDouble(old_key).intValue();
Integer ov = old_value;
if (ov != null) {
Map<String, Object> new_map = new HashMap<>();
new_map.put(new_key, old_value);
Map<String, Object> delete_old = new HashMap<>();
delete_old.put(old_key, FieldValue.delete());
batch.update(docRef, new_map);
batch.update(docRef, delete_old);
}
}
// Commit the batch
batch.commit().addOnCompleteListener(new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
// ...
}
});
} else {
// ... "Error updating field -> " + task.getException()
}
}
})
.addOnFailureListener(new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
// ... "Failure getting notices -> " + e
}
});
}
public void rename_date_field (final String old_key, final String new_key, final String collection_ref) {
FirebaseFirestore.getInstance().collection(collection_ref).get()
.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
#Override
public void onComplete(#NonNull Task<QuerySnapshot> task) {
if (task.isSuccessful()) {
WriteBatch batch = db.batch();
for (DocumentSnapshot document : task.getResult()) {
DocumentReference docRef = document.getReference();
Date old_value = document.getDate(old_key);
if (old_value != null) {
Map<String, Object> new_map = new HashMap<>();
new_map.put(new_key, old_value);
Map<String, Object> delete_old = new HashMap<>();
delete_old.put(old_key, FieldValue.delete());
batch.update(docRef, new_map);
batch.update(docRef, delete_old);
}
}
// Commit the batch
batch.commit().addOnCompleteListener(new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
// ...
}
});
} else {
// ... "Error updating field -> " + task.getException()
}
}
})
.addOnFailureListener(new OnFailureListener() {
#Override
public void onFailure(#NonNull Exception e) {
// ... "Failure getting notices -> " + e
}
});
}

Just wanted to share because I read that you were hoping for a Firestore based solution.
This worked for me. forEach will query each document in the collection and you can manipulate as you like.
db.collection("collectionName").get().then(function(querySnapshot) {
querySnapshot.forEach(async function(doc) {
await db.collection("collectionName").doc(doc.id).set({newField: value}, {merge: true});
// doc.data() is never undefined for query doc snapshots
console.log(doc.id, " => ", doc.data());
});
});

To solve this, you need to update each user to have the new property and for that I recommend you to use a Map. If you are using a model class when you are creating the users as explained in my answer from this post, to update all users, just iterate over the users collection amd use the following code:
Map<String, Object> map = new HashMap<>();
map.put("timestamp", FieldValue.serverTimestamp());
userDocumentReference.set(map, SetOptions.merge());

I am guessing that last_login is a primitive data type, maybe a long to hold a timestamp. An auto-generated setter would look like this:
private long last_login;
public void setLast_login(long last_login) {
this.last_login = last_login;
}
This leads to a crash when old documents that lack the field are fetched due to null assignment to a variable of a primitive data type.
One way around it is to modify your setter to pass in a variable of the equivalent wrapper class - Long instead of long in this case, and put a null check in the setter.
private long last_login;
public void setLast_login(Long last_login) {
if(last_login != null) {
this.last_login = last_login;
}
}
The cost of avoiding the null pointer exception is the boxing-unboxing overhead.