don't allow adding balance modification transaction when account already has other transaction

pkg/errs/transaction.go

@@ -12,4 +12,5 @@ var (
 	ErrTooMuchTransactionInOneSecond                       = NewNormalError(NORMAL_SUBCATEGORY_TRANSACTION, 6, http.StatusBadRequest, "too much transaction in one second")
 	ErrBalanceModificationTransactionCannotSetCategory     = NewNormalError(NORMAL_SUBCATEGORY_TRANSACTION, 7, http.StatusBadRequest, "balance modification transaction cannot set category")
 	ErrBalanceModificationTransactionCannotChangeAccountId = NewNormalError(NORMAL_SUBCATEGORY_TRANSACTION, 8, http.StatusBadRequest, "balance modification transaction cannot change account id")
+	ErrBalanceModificationTransactionCannotAddWhenNotEmpty = NewNormalError(NORMAL_SUBCATEGORY_TRANSACTION, 9, http.StatusBadRequest, "balance modification transaction cannot add when other transaction exists")
 )

pkg/services/transactions.go

@@ -200,8 +200,16 @@ func (s *TransactionService) CreateTransaction(transaction *models.Transaction)
 			return errs.ErrTransactionCategoryTypeInvalid
 		}
 
-		// Calculate balance modification transaction real amount
+		// Verify balance modification transaction and calculate real amount
 		if transaction.Type == models.TRANSACTION_TYPE_MODIFY_BALANCE {
+			otherTransactionExists, err := sess.Where("uid=? AND deleted=? AND destination_account_id=?", transaction.Uid, false, destinationAccount.AccountId).Limit(1).Exist(&models.Transaction{})
+
+			if err != nil {
+				return err
+			} else if otherTransactionExists {
+				return errs.ErrBalanceModificationTransactionCannotAddWhenNotEmpty
+			}
+
 			transaction.DestinationAmount = transaction.SourceAmount - destinationAccount.Balance
 		}