Fix update external id after validation

app/models/champs/rna_champ.rb

@@ -23,7 +23,7 @@ class Champs::RNAChamp < Champ
   validates :value, allow_blank: true, format: {
     with: /\AW[0-9]{9}\z/, message: I18n.t(:not_a_rna, scope: 'activerecord.errors.messages')
   }
-  after_validation :update_external_id, if: -> { value.present? && external_id.blank? }
+  after_validation :update_external_id, if: -> { value_changed? }
 
   delegate :id, to: :procedure, prefix: true
 
@@ -44,6 +44,6 @@ class Champs::RNAChamp < Champ
   end
 
   def update_external_id
-    update(external_id: value)
+    self.external_id = self.value
   end
 end