问题
I'm creating a Food ordering app.for that I'm saving the food names into the Food unique ID. So I created Item Details as a node, in this node has shopuniqueID as a child node, in this node has food uniqueID
this ID contains food details such as discount,itemname,price,discount If the User book the foods, which will be saved as below format
, If the customer confirms the food order after that user-selected quantity wants to delete from total item quantity, How can I delete two different values which are in the two different nodes?
This is my tried coding
btnorder=findViewById(R.id.qrbillid);
databaseReference= FirebaseDatabase.getInstance().getReference("User Booking").child(UserID).child(shopid);
dbrefcheck=FirebaseDatabase.getInstance().getReference("Item Details").child(shopid);
btnorder.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
databaseReference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
for(DataSnapshot dataSnapshot1:dataSnapshot.getChildren())
{
SelectedItems ui=dataSnapshot1.getValue(SelectedItems.class);
final String itemid=ui.getItemid();
final String Stritemselectedqty=ui.getItemid();
final String name=ui.getItemname();
///////////////////----find the user selection----////////////////////
dbrefcheck.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
for(DataSnapshot dataSnapshot2:dataSnapshot.getChildren())
{
UploadItem uploadItem=dataSnapshot2.getValue(UploadItem.class);
String uploadItemID=uploadItem.getKey();
String StrTotalqty=uploadItem.getQuantity();
if(itemid.equals(uploadItemID))
{
// do the mathematical operation
int totalqty=Integer.valueOf(StrTotalqty);
int selectedqty=Integer.valueOf(Stritemselectedqty);
int finalquality=totalqty-selectedqty;
Toast.makeText(MyBookedItems.this, ""+name+" ", Toast.LENGTH_SHORT).show();
}
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
///////////////////----find the user selection----////////////////////
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
});
回答1:
If We want to do mathematical operations between two node child values, We can't directly do that in Firebase Realtime Database.
- Retrieve the value from the Firebase
after that do the modification and again upload it.
private void updateQuantity(final String itemid, final String selecteditem) {
Query query4 = dbrefcheck .orderByChild("key") //key .equalTo(itemid); ValueEventListener valueEventListener = new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { for(DataSnapshot ds : dataSnapshot.getChildren()) { String qty=ds.child("quantity").getValue(String.class); int total=Integer.valueOf(qty); int sub=Integer.valueOf(selecteditem); int fv=total-sub; String sfv=String.valueOf(fv); Map<String, Object> map = new HashMap<>(); map.put("quantity", sfv); dbrefcheck.child(itemid).updateChildren(map).addOnCompleteListener(new OnCompleteListener<Void>() { @Override public void onComplete(@NonNull Task<Void> task) { } }).addOnSuccessListener(new OnSuccessListener<Void>() { @Override public void onSuccess(Void aVoid) { } }).addOnFailureListener(new OnFailureListener() { @Override public void onFailure(@NonNull Exception e) { } }); } } @Override public void onCancelled(@NonNull DatabaseError databaseError) { } }; query4.addListenerForSingleValueEvent(valueEventListener); } private void moveSelectedItemstoOrder(final DatabaseReference fromPath, final DatabaseReference toPath) { final String th=toPath.push().getKey(); fromPath.addListenerForSingleValueEvent(new ValueEventListener() { @Override public void onDataChange(final DataSnapshot dataSnapshot) { toPath.child(th).setValue(dataSnapshot.getValue(), new DatabaseReference.CompletionListener() { @Override public void onComplete(DatabaseError firebaseError, DatabaseReference firebase) { if (firebaseError != null) { Toast.makeText(MyBookedItems.this, "Try again", Toast.LENGTH_SHORT).show(); } else { StoreBookingDetails(th); } } }); } @Override public void onCancelled(DatabaseError databaseError) { } }); } private void DeleteValuefromSelectedItems() { databaseReference.setValue(null).addOnCompleteListener(new OnCompleteListener<Void>() { @Override public void onComplete(@NonNull Task<Void> task) { } }).addOnSuccessListener(new OnSuccessListener<Void>() { @Override public void onSuccess(Void aVoid) { } }).addOnFailureListener(new OnFailureListener() { @Override public void onFailure(@NonNull Exception e) { } }); } private void StoreBookingDetails(final String keytostore) { //////////////////------------retrive data-------------//////////////////////////////some these methods are unnecessary but i remove some code savedata(keytostore); //////////////////------------retrive data-------------////////////////////////////// } private void savedata(String keytostore) { String status="Order Request"; // shopid ----> BookingDetails bd=new BookingDetails(keytostore,currentdate,UserID,subtotal,status,f1,f2,f3,currentTime); dbbookingDetails.child(keytostore).setValue(bd).addOnCompleteListener(new OnCompleteListener<Void>() { @Override public void onComplete(@NonNull Task<Void> task) { if(task.isSuccessful()) { DeleteValuefromSelectedItems(); }else { Toast.makeText(MyBookedItems.this, "Check the intenet connection", Toast.LENGTH_SHORT).show(); } } }).addOnSuccessListener(new OnSuccessListener<Void>() { @Override public void onSuccess(Void aVoid) { } }).addOnFailureListener(new OnFailureListener() { @Override public void onFailure(@NonNull Exception e) { } }); /////////////////////////////--------------------///////////////////////////////// UserBookingDetails ubd=new UserBookingDetails(shopname,shopid,shopphnno,keytostore,UserID,subtotal,currentdate,currentTime,"Order Sent","",""); dbbookingdetailsUser.child(keytostore).setValue(ubd).addOnCompleteListener(new OnCompleteListener<Void>() { @Override public void onComplete(@NonNull Task<Void> task) { } }).addOnSuccessListener(new OnSuccessListener<Void>() { @Override public void onSuccess(Void aVoid) { AlertDialog.Builder adb = new AlertDialog.Builder(MyBookedItems.this); adb.setTitle("Booking Successful"); adb.setPositiveButton("View History", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialogInterface, int i) { startActivity(new Intent(MyBookedItems.this,OrderHistory.class)); } }); adb.setNegativeButton("Cancel", new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int which) { finish(); } }); adb.show(); } }).addOnFailureListener(new OnFailureListener() { @Override public void onFailure(@NonNull Exception e) { } });
来源：https://stackoverflow.com/questions/60968183/how-to-subtract-two-different-node-child-values-in-firebase-realtime-databse