How to autoincrement userID in Firestore?

Question

So I created a booking app which sends data into booking collection taking userID as Document Name. But when the user books again it overwrites the previous booking userID document. What I want to do is: 1) Implement autoincrement on userID, and also 2) display the autoincremented booking too (Notice I'm using userID because I want to keep it unique to that user only). 3) I also want to implement a limit on booking if someone can help with that.

Firestore Firebase Image:

The code to send data into BOOKING COLLECTION and creating DOCUMENT with userID:

public class bookingpage extends AppCompatActivity {

EditText mFirstnamelastname,mMobnum,mPincode,mFlatno,mArea,mLandmark,mTown,mState;

Button mBook;
String userID;
FirebaseAuth fAuth;
FirebaseFirestore fstore;
ProgressBar progressBar;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_bookingpage);

    //pickup
    mFirstnamelastname=findViewById(R.id.firstlastname);
    mMobnum=findViewById(R.id.mobnum);
    mPincode=findViewById(R.id.pincode);
    mFlatno=findViewById(R.id.flatno);
    mArea=findViewById(R.id.area);
    mLandmark=findViewById(R.id.landmark);
    mTown=findViewById(R.id.town);
    mState=findViewById(R.id.state);
    

    mBook=findViewById(R.id.editbook);
    progressBar=findViewById(R.id.progressBar4);

    fAuth=FirebaseAuth.getInstance();
    fstore=FirebaseFirestore.getInstance();

    mBook.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            //pickup
            String firstname = mFirstnamelastname.getText().toString().trim();
            String phoneno   = mMobnum.getText().toString().trim();
            String pincode   = mPincode.getText().toString().trim();
            String flatno   = mFlatno.getText().toString().trim();
            String area   = mArea.getText().toString().trim();
            String landmark   = mLandmark.getText().toString().trim();
            String town      = mTown.getText().toString().trim();
            String state     = mState.getText().toString().trim();
     
           
            progressBar.setVisibility(View.VISIBLE);

             //saving data
            userID=fAuth.getCurrentUser().getUid();
            //creating a document reference creating a collection booking and making a new doc using user id
            DocumentReference documentReference = fstore.collection("Booking").document(userID);
            //creating a hashmap to send data
            Map<String,Object> book = new HashMap<>();
            //setting status
            book.put("Status -","Active");
            //pickup
            book.put("a1 - Fullname",firstname);
            book.put("a2 - PhoneNo",phoneno);
            book.put("a3 - Pincode",pincode);
            book.put("a4 - Flatno",flatno);
            book.put("a5 - Area",area);
            book.put("a6 - Landmark",landmark);
            book.put("a7 - Town",town);
            book.put("a8 - State",state);
           

            //using the document reference to set user document
            documentReference.set(book).addOnSuccessListener(new OnSuccessListener<Void>() {
                @Override
                public void onSuccess(Void aVoid) {
                    Toast.makeText(bookingpage.this, "Booking Successful", Toast.LENGTH_SHORT).show();
                    Log.d("Tag","onSuccess: Successfully booked for "+ userID);
                    startActivity(new Intent(getApplicationContext(),MainActivity2.class));
                    finish();
                }
            }).addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {
                    Toast.makeText(bookingpage.this, "Error!" + e.getMessage(), Toast.LENGTH_LONG).show();
                }
            });

            progressBar.setVisibility(View.INVISIBLE);
        }
    });
}

}

The code to display the booking collection's document with userID:

        final DocumentReference documentReference = fstore.collection("Booking").document(userID);
        documentReference.addSnapshotListener(this, new EventListener<DocumentSnapshot>() {
                @Override
                public void onEvent(@Nullable DocumentSnapshot documentSnapshot, @Nullable FirebaseFirestoreException e) {
                    //putting if else fixed crashing
                    if (e != null) {
                        Log.d("Tag", "Error:" + e.getMessage());
                    } else {
                       

                        mStatus.setText(documentSnapshot.getString("Status -"));


                        mFirstnamelastname.setText(documentSnapshot.getString("a1 - Fullname"));

                        mMobnum.setText(documentSnapshot.getString("a2 - PhoneNo"));

                        mPincode.setText(documentSnapshot.getString("a3 - Pincode"));

                        mFlatno.setText(documentSnapshot.getString("a4 - Flatno"));

                        mArea.setText(documentSnapshot.getString("a5 - Area"));

                        mLandmark.setText(documentSnapshot.getString("a6 - Landmark"));

                        mTown.setText(documentSnapshot.getString("a7 - Town"));

                        mState.setText(documentSnapshot.getString("a8 - State"));

                    }


                }
            });

I'm a beginner please try to explain your answer so that I can understand & learn more :)

Answer 1

Well... you just shouldn't use the UserId's as document names in the Booking collection. It's just goes against logic and best-practices.

You should instead let Firestore create a BookingId. It would be your current booking document + a new field (String) holding the UserId of the user who made the booking.

This would be a more logical (and scalable) way.

To limit the number of bookings, you could add a field in your UserId documents (in users collection), called bookingCount (Integer). Each time a User books, check if the bookingCount >= bookingLimit (arbitrary value of your choosing).

If bookingCount < bookingLimit, then allow them to book and increment the bookingCount by 1.