Fix ActiveRecord ObjectExtension has_one setter breaks with custom pr…

…imary key class

Fixes #3460

lib/rails_admin/adapters/active_record/object_extension.rb

@@ -13,7 +13,7 @@ def #{association.name}_id
                 end
 
                 def #{association.name}_id=(item_id)
-                  self.#{association.name} = #{association.klass}.find_by_id(item_id)
+                  self.#{association.name} = (#{association.klass}.find(item_id) rescue nil)
                 end
               RUBY
             end

spec/dummy_app/app/active_record/league.rb

@@ -2,6 +2,7 @@ class League < ActiveRecord::Base
   has_many :divisions, foreign_key: 'custom_league_id'
   has_many :teams, -> { readonly }, through: :divisions
   has_many :players, through: :teams
+  has_one :division, foreign_key: 'custom_league_id'
 
   validates_presence_of(:name)
 

spec/rails_admin/adapters/active_record/object_extension_spec.rb

@@ -56,5 +56,16 @@ class PlayerWithAutoSave < Player
         expect(user.reload.team).to eq team
       end
     end
+
+    context 'when associated class has custom primary key' do
+      let(:league) { FactoryBot.build(:league).extend(RailsAdmin::Adapters::ActiveRecord::ObjectExtension) }
+      let(:division) { FactoryBot.create :division }
+
+      it 'does not break' do
+        league.division_id = division.id
+        league.save!
+        expect(league.reload.division).to eq division
+      end
+    end
   end
 end