Relations and vehicles reference each other

models/concerns/expand_data.rb

@@ -50,6 +50,9 @@ def add_relation_references
       relation.linked_services.each{ |service|
         service.relations << relation
       }
+      relation.linked_vehicles.each{ |vehicle|
+        vehicle.relations << relation
+      }
     }
   end
 

models/relation.rb

@@ -24,6 +24,7 @@ class Relation < Base
     field :linked_ids, default: []
     has_many :linked_services, class_name: 'Models::Service'
     field :linked_vehicle_ids, default: []
+    has_many :linked_vehicles, class_name: 'Models::Vehicle'
     field :periodicity, default: 1
 
     # ActiveHash doesn't validate the validator of the associated objects

models/vehicle.rb

@@ -104,6 +104,7 @@ class Vehicle < Base
     has_many :capacities, class_name: 'Models::Capacity'
     # include ValidateTimewindows # <- This doesn't work
     has_many :rests, class_name: 'Models::Rest'
+    has_many :relations, class_name: 'Models::Relation'
 
     def self.create(hash)
       if hash[:sequence_timewindows]&.size&.positive? && hash[:unavailable_days]&.size&.positive? # X&.size&.positive? is not the same as !X&.empty?