Fix double binding issue

app/models/bank_transaction.rb

@@ -30,6 +30,8 @@ class BankTransaction < ActiveRecord::Base
     invoice = registrar.invoices.find_by(id: invoice_id)
     return unless invoice
 
+    return if invoice.binded?
+
     return if invoice.sum != sum
     create_account_activity(
       account: registrar.cash_account,

app/models/invoice.rb

@@ -2,11 +2,17 @@ class Invoice < ActiveRecord::Base
   belongs_to :seller, class_name: 'Registrar'
   belongs_to :buyer, class_name: 'Registrar'
   has_many :invoice_items
+  has_one :account_activity
+
   accepts_nested_attributes_for :invoice_items
 
   validates :invoice_type, :due_date, :currency, :seller_name,
             :seller_iban, :buyer_name, :invoice_items, :vat_prc, presence: true
 
+  def binded?
+    account_activity.present?
+  end
+
   def to_s
     I18n.t('invoice_no', no: id)
   end

spec/models/bank_statement_spec.rb

@@ -50,7 +50,7 @@ describe BankStatement do
           description: 'Invoice no. 1'
         }),
         Fabricate(:bank_transaction, {
-          sum: 120.0,
+          sum: 240.0,
           reference_no: 'RF7086666663',
           description: 'Invoice no. 1'
         })
@@ -66,6 +66,7 @@ describe BankStatement do
       r.cash_account.balance.should == 240.0
 
       bs.bank_transactions.unbinded.count.should == 1
+      bs.partially_binded?.should == true
     end
 
     # it 'should have one version' do