fix: belongs_to field should use association primary_key

lib/avo/fields/belongs_to_field.rb

@@ -127,7 +127,7 @@ def values_for_type(model = nil)
         end
 
         query.all.map do |record|
-          [resource.new(record: record).record_title, record.to_param]
+          [resource.new(record: record).record_title, record.send(primary_key)]
         end
       end
 
@@ -157,6 +157,10 @@ def is_polymorphic?
         false
       end
 
+      def primary_key
+        @primary_key ||= reflection.association_primary_key
+      end
+
       def foreign_key
         @foreign_key ||= if polymorphic_as.present?
           polymorphic_as
@@ -211,12 +215,12 @@ def fill_field(record, key, value, params)
           if valid_model_class.blank? || id_from_param.blank?
             record.send(:"#{polymorphic_as}_id=", nil)
           else
-            record_id = target_resource(record:, polymorphic_model_class: value.safe_constantize).find_record(id_from_param).id
+            record_id = target_resource(record:, polymorphic_model_class: value.safe_constantize).find_record(id_from_param).send(primary_key)
 
             record.send(:"#{polymorphic_as}_id=", record_id)
           end
         else
-          record_id = value.blank? ? value : target_resource(record:).find_record(value).id
+          record_id = value.blank? ? value : target_resource(record:).find_record(value).send(primary_key)
 
           record.send(:"#{key}=", record_id)
         end