(defclass restore-to-data-structure-mixin ()
  ())

(defclass some-class (restore-to-data-structure-mixin)
  ())

(defclass some-class2 (restore-to-data-structure-mixin)
  ())

(defgeneric restore-to-data-structure (object))

(defmethod initialize-instance :around ((uninitialized restore-to-data-structure-mixin) &rest initargs
					&key ((restore-to-data-structure restore-to-data-structure))
					&allow-other-keys)
  (declare (ignore initargs))
  (let ((initialized-instance (call-next-method)))
    (when restore-to-data-structure
      (restore-to-data-structure initialized-instance)
      initialized-instance)))

;;; now we don't have to bother with initialize-instance :around for each class
;;; it's enough for all of them to inherit restore-to-data-structure-mixin and have
;;; restore-to-data-structure methods defined

(defmethod restore-to-data-structure ((object some-class))
  (format t "~A was read from the database and restored into the right data structure.~%" object))

(defmethod restore-to-data-structure ((object some-class2))
  (format t "~A was read from the database and restored etc similar story~%" object))

(make-instance 'some-class) ; no output on *standard-output*
(make-instance 'some-class 'restore-to-data-structure t) ; #<SOME-CLASS {1007378873}> was read from the database and restored into the right data structure. 
(make-instance 'some-class2 'restore-to-data-structure t) ; #<SOME-CLASS2 {1005668B53}> was read from the database and restored etc similar story