Fix connection issues when initializing ActiveRecord Abstract models (#…

…3470)

When initializing abstract (ActiveRecord) models, #table_exists? is used and calls through the connection, which (in the case of a precompile step) can raise errors other than the ActiveRecord::NoDatabaseError that's currently handled.

lib/rails_admin/abstract_model.rb

@@ -19,7 +19,7 @@ def all(adapter = nil)
       def new(m)
         m = m.constantize unless m.is_a?(Class)
         (am = old_new(m)).model && am.adapter ? am : nil
-      rescue *([LoadError, NameError] + (defined?(ActiveRecord) ? ['ActiveRecord::NoDatabaseError'.constantize] : []))
+      rescue *([LoadError, NameError] + (defined?(ActiveRecord) ? ['ActiveRecord::NoDatabaseError'.constantize, 'ActiveRecord::ConnectionNotEstablished'.constantize] : []))
         puts "[RailsAdmin] Could not load model #{m}, assuming model is non existing. (#{$ERROR_INFO})" unless Rails.env.test?
         nil
       end

spec/rails_admin/abstract_model_spec.rb

@@ -21,6 +21,16 @@
         expect(RailsAdmin::AbstractModel.new('WithoutTable')).to eq nil
       end
     end
+
+    context 'on ActiveRecord::ConnectionNotEstablished', active_record: true do
+      before do
+        expect(WithoutTable).to receive(:table_exists?).and_raise(ActiveRecord::ConnectionNotEstablished)
+      end
+
+      it 'does not raise error and returns nil' do
+        expect(RailsAdmin::AbstractModel.new('WithoutTable')).to eq nil
+      end
+    end
   end
 
   describe '#to_s' do