Android Firestore Convert Array of Document References to List<Pojo>

Android Firestore convert array of document references to ListPojo

Yes it is. Please see the following lines of code:

FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
if (firebaseUser != null) {
    String uid = firebaseUser.getUid();
    rootRef.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()) {
                    List<DocumentReference> list = (List<DocumentReference>) document.get("bookmarks");
                    List<Task<DocumentSnapshot>> tasks = new ArrayList<>();
                    for (DocumentReference documentReference : list) {
                        Task<DocumentSnapshot> documentSnapshotTask = documentReference.get();
                        tasks.add(documentSnapshotTask);
                    }
                    Tasks.whenAllSuccess(tasks).addOnSuccessListener(new OnSuccessListener<List<Object>>() {
                        @Override
                        public void onSuccess(List<Object> list) {
                            //Do what you need to do with your list
                            for (Object object : list) {
                                TeacherPojo tp = ((DocumentSnapshot) object).toObject(TeacherPojo.class);
                                Log.d("TAG", tp.getFirstName());
                            }
                        }
                    });
                }
            }
        }
    });
}

So the List<Object> list is actually the list that contains objects of type TeacherPojo.

Firestore document object (documentSnapshot) to POJO with nested maps

As you already say voucher is a Map, so that's what you should use in your Java class too:

public class MyPOJO {

    public String id;
    public Map<String,Voucher> vouchers;

}

public class Voucher {

    public String name, description;

}

Firebase Firestore : How to convert document object to a POJO on Android

With a DocumentSnapshot you can do:

DocumentSnapshot document = future.get();
if (document.exists()) {
    // convert document to POJO
    NotifPojo notifPojo = document.toObject(NotifPojo.class);
}

How to map document Reference to POJO in firestore firebase for kotlin

You are getting the following error:

java.lang.RuntimeException: Could not deserialize object. Can't convert object of type com.google.firebase.firestore.DocumentReference to type com.firestorepoc.model.Biomarker

Because you have declared the content property in your Biomarkers class to be of type Biomarker, while in the database is actually a DocumentReference. So the exception is raised because there is no way in Kotlin in which you can cast an object of type DocumentReferenc to an object of type Biomarker.

To solve this, you have to change the content property to be of type DocumentReference as it is in your database.

Besides that, I see that the biomarkers property is an array. If you need to map that array to a list of Biomarkers objects (List<Biomarkers>), please check out the following article:

• How to map an array of objects from Cloud Firestore to a List of objects?

Android Firestore querying particular value in Array of Objects

With your current document structure, it's not possible to perform the query you want. Firestore does not allow queries for individual fields of objects in list fields.

What you would have to do is create an additional field in your document that is queryable. For example, you could create a list field with only the list of string languages that are part of the document. With this, you could use an array-contains query to find the documents where a language is mentioned at least once.

For the document shown in your screenshot, you would have a list field called "languages" with values ["Swift", "Kotlin"].

Cast result of multiple tasks list to their POJO in Tasks.whenAllSuccess() (Firestore)

As I understand, you have two types of lists, userModelArrayList which is of type UserModel, and likeModelArrayList which is of type LikeModel. To be able to add each object in its corresponding type of list, you should create the lists of Task objects to be of type UserModel and LikeModel. So please change the following lines of code:

List<Task<DocumentSnapshot>> fetchUserTasks = new ArrayList<>();
List<Task<DocumentSnapshot>> fetchLikeTasks = new ArrayList<>();

to

List<Task<UserModel>> fetchUserTasks = new ArrayList<>();
List<Task<LikeModel>> fetchLikeTasks = new ArrayList<>();

So instead of adding the DocumentSnapshot objects, add the actual objects. So use toObject() before. That being said, you can then check each object type using instanceof operator, like in the following lines of code:

Tasks.whenAllSuccess(combineUserTasks, combineLikeTask).addOnSuccessListener(new OnSuccessListener<List<Object>>() {
    @Override
    public void onSuccess(List<Object> objects) {
        for (Object object : objects) {
            if (object instanceof UserModel) {
                userModelArrayList.add(userModel);
            } else if (object instanceof LikeModel) {
                likeModelArrayList.add(likeModel);
            }
        }
    }
});

Now, you'll have each list populated with the corresponding object type.

Firestore query on collection

According to your last comment, I understand that you want to get all documents within a single collection and not to query multiple collections, which is not possbile for the moment in Firestore.

If you have a list of ids, then simply iterate over it and create for each id in the list the corresponding DocumentReference and then add all those references to a List<DocumentReference>. After that, iterate over the new list and for each reference create a Task and then add all those Tasks objects to List<Task<DocumentSnapshot>>.

In the end, just pass the list of Tasks to Tasks's whenAllSuccess() method:

Tasks.whenAllSuccess(tasks).addOnSuccessListener(new OnSuccessListener<List<Object>>() {
    @Override
    public void onSuccess(List<Object> list) {
        //Do what you need to do with your list
        for (Object object : list) {
            YourObject yb = ((DocumentSnapshot) object).toObject(YourObject.class);
            Log.d("TAG", yb.getPropertyName);
        }
    }
});

In code it looks like my answer from this post:

• Android Firestore convert array of document references to List<Pojo>

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