var trans:Transaction = Firestore.createTransaction();
 if(trans)
 {
     myTransaction = trans;
      
     myTransaction.addEventListener(FirestoreEvents.TRANSACTION_BEGIN, onTransactionBegin);
     myTransaction.addEventListener(FirestoreEvents.TRANSACTION_COMPLETE, onTransactionComplete);
     myTransaction.addEventListener(FirestoreEvents.TRANSACTION_FAILURE, onTransactionFailure);
      
     // to start working with the transaction, you must wait for the "TRANSACTION_BEGIN" event to happen
     myTransaction.execute();
 }
 else
 {
     // Every transaction will be finished when you call either of these methods:
     // myTransaction.abort();
     // myTransaction.keep();
     trace("another transaction is not released yet");
 }
  
 function onTransactionBegin(e:FirestoreEvents):void
 {
     trace(">> onTransactionBegin");
      
     // If you want to read more that one DocumentReference, you must read each inside the prior onReadComplete functions.
     myTransaction.read(myDocument, onReadComplete);
 }
  
 function onReadComplete($snapshot:DocumentSnapshot, $err:String):void
 {
     if($err)
     {
         trace("could not read the document: " + $err);
         myTransaction.abort();
     }
     else
     {
         trace("ReadSuccess, data: " + JSON.stringify($snapshot.data));
          
         // increment the current value in database
         var newValue:int = $snapshot.data.population + 1;
          
          
         if(newValue > 1000000)
         {
             trace("value is more than what our game needs.");
             myTransaction.abort();
         }
         else
         {
              
             // payload message will be delivered to the TRANSACTION_COMPLETE event.
             // you must change your UI based on this message known as the transaction outcome.
             // in our example, you must not use the "newValue" value to change your UI, instead
             // you must pass it through the "keep()" method and change your UI when TRANSACTION_COMPLETE
             // happens.
              
             myTransaction.outcome = "payload message which can be anything for example a json String";
             myTransaction.update(myDocument, {population:newValue}, onUpdateComplete);
         }
     }
 }
  
 function onUpdateComplete():void
 {
      
     // You must call the "keep" method when you are sure the "write, update or omit" commands have
     // finished their job. In this example, we are calling the "keep" method when the last "update"
     // method is finished through "onUpdateComplete"
      
     myTransaction.keep();
 }
  
 function onTransactionComplete(e:FirestoreEvents):void
 {
     trace("onTransactionComplete: " + e.transactionOutcome);
      
     myTransaction.removeEventListener(FirestoreEvents.TRANSACTION_BEGIN, onTransactionBegin);
     myTransaction.removeEventListener(FirestoreEvents.TRANSACTION_COMPLETE, onTransactionComplete);
     myTransaction.removeEventListener(FirestoreEvents.TRANSACTION_FAILURE, onTransactionFailure);
 }
  
 function onTransactionFailure(e:FirestoreEvents):void
 {
     trace("onTransactionFailure: " + e.msg);
      
     myTransaction.removeEventListener(FirestoreEvents.TRANSACTION_BEGIN, onTransactionBegin);
     myTransaction.removeEventListener(FirestoreEvents.TRANSACTION_COMPLETE, onTransactionComplete);
     myTransaction.removeEventListener(FirestoreEvents.TRANSACTION_FAILURE, onTransactionFailure);
 }