code: def fixed_attributes
        if model_class
          presence_validators = model_class.validators.detect { |x| x.kind_of?(ActiveRecord::Validations::PresenceValidator) }
        end
        # Attributes that has to be always on the entity, so attributes making unique index of the record + attributes
        # that have presence validation
        fixed_attributes = manager_ref
        fixed_attributes += presence_validators.attributes if presence_validators.present?
        fixed_attributes
      end
docs: Attributes that are needed to be able to save the record, i.e. attributes that are part of the unique index
   and attributes with presence validation or NOT NULL constraint
  
   @return [Array<Symbol>] attributes that are needed for saving of the record