Fix belongs_to_required_by_default call for Mongoid

Author: RaymondFFT

lib/rails_admin/adapters/active_record.rb

@@ -135,6 +135,10 @@ def parse_id(id)
         end
       end
 
+      def belongs_to_required_by_default
+        model.belongs_to_required_by_default
+      end
+
     private
 
       def primary_key_scope(scope, id)

lib/rails_admin/adapters/mongoid.rb

@@ -112,6 +112,10 @@ def adapter_supports_joins?
         false
       end
 
+      def belongs_to_required_by_default
+        Mongoid.belongs_to_required_by_default
+      end
+
     private
 
       def build_statement(column, type, value, operator)

lib/rails_admin/config/fields/base.rb

@@ -225,13 +225,9 @@ def filter_options
             end || model.reflect_on_all_associations(:belongs_to).detect do |a|
               next unless a.name == column_name
 
-              if a.options.key?(:required)
-                !!a.options[:required]
-              elsif a.options[:optional].nil?
-                model.belongs_to_required_by_default
-              else
-                !a.options[:optional]
-              end
+              required = a.options[:required] if a.options.key?(:required)
+              required = !a.options[:optional] if a.options.key?(:optional) && required.nil?
+              required.nil? ? abstract_model.belongs_to_required_by_default : required
             end
           end
         end