reverse transaction with negative amount

app/controllers/concerns/transactions_query.rb

@@ -12,7 +12,6 @@ class TransactionsQuery
   def query
     Arel::SelectManager.new(ActiveRecord::Base)
       .from(arel)
-      .order(@arel_table[:time].desc)
   end
 
   def arel

app/controllers/transactions_controller.rb

@@ -1,20 +1,20 @@
 class TransactionsController < ApplicationController
-  load_and_authorize_resource
   skip_before_filter :verify_authenticity_token, only: :create
 
   before_action :authenticate_user!, except: :create
   before_action :authenticate_user_or_client!, only: :create
   respond_to :js, only: :create
 
-  def index
-    @transactions = Transaction.all
-  end
-
   def create
+    @transaction = Transaction.new(transaction_params)
+    @transaction.reverse if @transaction.amount < 0
+    authorize!(:create, @transaction)
+
     if @transaction.save
       head :created
     else
-      render json: @transaction.errors.full_messages, status: :unprocessable_entity
+      render json: @transaction.errors.full_messages,
+        status: :unprocessable_entity
     end
   end
 

app/models/transaction.rb

@@ -24,13 +24,6 @@ class Transaction < ActiveRecord::Base
   validates :amount, numericality: { greater_than: 0 }
   validate :different_debtor_creditor
 
-  def initialize *args, **kwargs
-    super *args, **kwargs
-    if amount < 0
-      self.creditor, self.debtor = debtor, creditor
-      self.amount = self.amount.abs
-    end
-  end
 
   def peer_of(user)
     return creditor if user == debtor
@@ -42,6 +35,11 @@ class Transaction < ActiveRecord::Base
     return amount if user == creditor
   end
 
+  def reverse
+    self.creditor, self.debtor = self.debtor, self.creditor
+    self.amount *= -1
+  end
+
   private
 
   def recalculate_balances

spec/models/transaction_spec.rb

@@ -35,5 +35,4 @@ RSpec.describe Transaction, type: :model do
       expect {trans.save!}.to change {@user.balance}.by(-10)
     end
   end
-
 end