Fix polymorphic association target classes not set correctly in subclasses

Fixes #3631

Author: mshibuya

lib/rails_admin/adapters/active_record/association.rb

@@ -33,7 +33,7 @@ def field_type
 
         def klass
           if options[:polymorphic]
-            polymorphic_parents(:active_record, model.name.to_s, name) || []
+            polymorphic_parents(:active_record, association.active_record.name.to_s, name) || []
           else
             association.klass
           end

lib/rails_admin/adapters/mongoid/association.rb

@@ -46,7 +46,7 @@ def field_type
 
         def klass
           if polymorphic? && %i[referenced_in belongs_to].include?(macro)
-            polymorphic_parents(:mongoid, model.name, name) || []
+            polymorphic_parents(:mongoid, association.inverse_class_name, name) || []
           else
             association.klass
           end

spec/rails_admin/adapters/active_record/association_spec.rb

@@ -215,6 +215,18 @@ class FieldTestWithSymbolForeignKey < FieldTest
       expect(@category.associations.detect { |a| a.name == :librarian }.klass).to eq [ARUser]
       expect(@blog.associations.detect { |a| a.name == :librarian }.klass).to eq [ARProfile]
     end
+
+    describe 'on a subclass' do
+      before do
+        class ARReview < ARComment; end
+        allow(RailsAdmin::Config).to receive(:models_pool).and_return(%w[ARBlog ARPost ARCategory ARUser ARProfile ARComment ARReview])
+      end
+      subject { RailsAdmin::AbstractModel.new(ARReview).associations.detect { |a| a.name == :commentable } }
+
+      it 'returns correct target klasses' do
+        expect(subject.klass).to eq [ARBlog, ARPost]
+      end
+    end
   end
 
   describe 'polymorphic inverse has_many association' do

spec/rails_admin/adapters/mongoid/association_spec.rb

@@ -168,6 +168,18 @@ class MongoNote
       expect(subject.read_only?).to be_falsey
       expect(subject.nested_options).to be_nil
     end
+
+    describe 'on a subclass' do
+      before do
+        class MongoReview < MongoComment; end
+        allow(RailsAdmin::Config).to receive(:models_pool).and_return(%w[MongoBlog MongoPost MongoCategory MongoUser MongoProfile MongoComment MongoReview])
+      end
+      subject { RailsAdmin::AbstractModel.new(MongoReview).associations.detect { |a| a.name == :commentable } }
+
+      it 'returns correct target klasses' do
+        expect(subject.klass).to eq [MongoBlog, MongoPost]
+      end
+    end
   end
 
   describe 'polymorphic inverse has_many association' do