define PersistentVolumeClaim#persistent_volume as a relation

app/models/persistent_volume_claim.rb

@@ -2,16 +2,14 @@ class PersistentVolumeClaim < ApplicationRecord
   belongs_to :ext_management_system, :foreign_key => "ems_id"
   belongs_to :container_project
   has_many :container_volumes
+  has_one :persistent_volume, -> { where(:type => 'PersistentVolume')}, :class_name => "ContainerVolume"
+
   serialize :capacity, Hash
   serialize :requests, Hash
   serialize :limits, Hash
 
   virtual_column :storage_capacity, :type => :integer
 
-  def persistent_volume
-    container_volumes.find_by_type('PersistentVolume')
-  end
-
   def storage_capacity
     capacity[:storage]
   end

spec/models/persistent_volume_claim_spec.rb

@@ -18,4 +18,19 @@
       expect(persistent_volume.storage_capacity).to be nil
     end
   end
+
+  describe "#persistent_volume" do
+    it "finds none" do
+      pvc = FactoryBot.create(:persistent_volume_claim)
+      FactoryBot.create(:container_volume, :persistent_volume_claim => pvc)
+      expect(pvc.persistent_volume).to be_nil
+    end
+
+    it "finds one" do
+      pvc = FactoryBot.create(:persistent_volume_claim)
+      FactoryBot.create(:container_volume, :persistent_volume_claim => pvc)
+      pv = FactoryBot.create(:persistent_volume, :persistent_volume_claim => pvc)
+      expect(pvc.persistent_volume).to eq(pv)
+    end
+  end
 end