Add methods to retrieve invoices and estimates for vehicles

app/models/vehicle.rb

@@ -72,6 +72,16 @@ class Vehicle < ActiveRecord::Base
     self.name = to_s
   end
 
+  # reurns all invoices for this vehicle
+  def invoices
+    self.issues.flat_map(&:invoices).uniq
+  end
+
+  # returns all estimates for this vehicle
+  def estimates
+    self.issues.flat_map(&:estimate).uniq
+  end
+  
   private
   
   # init method to pull JSON details from NHTSA