Order Firestore data by TimeStamp in Ascending order

Question

I am storing Ideas posted by the application in Firestore. The data is stored in Firestore like this Ideas/{documentID}/IdeaObject. The issue is when I retrieve the data it is not sorted w.r.t time it was posted. The ideas that are retrieved are in according to the id's of their documentID which is automatically create by Firestore. I have used ServerTimestamp in my Model Class and also when I retrieve it, I use the orderBy method with my Firestore reference but still nothing.

Idea.java

public class Idea {
    @ServerTimestamp
    private Date date;
    private String title, idea, timeCommitment, ideaStage, postedBy, website, videoPitch;
    private int views, favorites;
    private ArrayList<String> lookingFor = new ArrayList<>();
    private ArrayList<String> tags = new ArrayList<>();
    private String userID;
    private String timeStamp;

    public Idea() {
    }

    public Idea(String title, String idea, String timeCommitment, String ideaStage, String postedBy, String website, String videoPitch, int views, int favorites, ArrayList<String> lookingFor, ArrayList<String> tags, String userID, String timeStamp) {
        this.title = title;
        this.idea = idea;
        this.timeCommitment = timeCommitment;
        this.ideaStage = ideaStage;
        this.postedBy = postedBy;
        this.website = website;
        this.videoPitch = videoPitch;
        this.views = views;
        this.favorites = favorites;
        this.lookingFor = lookingFor;
        this.tags = tags;
        this.userID = userID;
        this.timeStamp = timeStamp;
    }

Ideas Posting Method

  private void postIdea() {

        final String ideaID = UUID.randomUUID().toString();
        final SimpleDateFormat sdf = new SimpleDateFormat("yyyy.MM.dd.HH.mm.ss");
        Timestamp timestamp = new Timestamp(System.currentTimeMillis());


        Idea ideas = new Idea(title, idea, timeCommitment, ideaStage, AppValues.fullName, website, videoPitch, 0, 0, lookingFor, tags, AppValues.userId, "" + timestamp.getTime());

        firestoreDb.collection("ideas")
                .document(ideaID)
                .set(ideas)
                .addOnSuccessListener(new OnSuccessListener<Void>() {
                    @Override
                    public void onSuccess(Void aVoid) {
                        postIdeaUser(ideaID);
                    }
                })
                .addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        hideLoadingDialog();
                        showToast(e.getMessage());
                    }
                });
    }

Retrieving all Ideas by Time

   firestoreDb.collection("ideas")
                .orderBy("timeStamp", Query.Direction.ASCENDING)
                .get()
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()) {

                            ideaArrayList = new ArrayList<>();
                            ideaArrayList.clear();

                            for (DocumentSnapshot documentSnapshot : task.getResult()) {
                                Idea idea = documentSnapshot.toObject(Idea.class);
                                if (!idea.getUserID().equals(AppValues.userId)) {
                                    ideaArrayList.add(idea);
                                }
                            }

                            callAdapter();

                        } else {
                            Log.d(TAG, "Error getting documents: ", task.getException());
                            progressBar.setVisibility(View.GONE);
                            swipeRefresh.setEnabled(true);
                            errorText.setVisibility(View.VISIBLE);
                        }
                    }
                }); 

What I want to achieve is retrieve all the ideas and have them ordered ascending by the TimeStamp value.

Solution 1

You cannot use a String (timeStamp) when querying your database instead of a Date (date) and expect to behave as it was a date. So to solve this, please change the following line of code:

firestoreDb.collection("ideas")
            .orderBy("timeStamp", Query.Direction.ASCENDING)

to

firestoreDb.collection("ideas")
            .orderBy("date", Query.Direction.ASCENDING)

To make it work, this kind of query requires an index. To create one, please check my answer from the following post:

• Firestore whereEqualTo, orderBy and limit(1) not working

Solution 2

In my case, the vanilla version would be,

firestoreDb.collection("ideas")
     .orderBy("timestamp", "asc")

firestoreDb.collection("ideas")
     .orderBy("timestamp", "desc")

"ideas" is the name of your collection

"timestamp" is the key or field or column name to be used for sorting.

"asc" or "desc" is the option to be used for the order

Solution 3

You have to also add index in your firebase account which is in database -> Indexes -> add index