Memento pattern in LLD - Architecture Diagram

System Overview - Memento pattern

The Memento pattern helps save and restore an object's state without exposing its internal details. It is useful when you want to implement undo or rollback features in applications.

Key requirements include capturing the object's state, storing it safely, and restoring it on demand without breaking encapsulation.

Architecture Diagram

User
  |
  v
Originator <--> Memento
  |
  v
Caretaker

Components

User

actor

Initiates commands to save or restore state

Originator

service

Creates a memento capturing its current state and restores state from a memento

Memento

data_object

Stores the internal state of the Originator without exposing details

Caretaker

manager

Keeps track of mementos and manages saving/restoring without inspecting state

Request Flow - 6 Hops

User → Originator

Originator → Memento

Originator → Caretaker

User → Caretaker

Caretaker → Originator

Originator → Originator

Failure Scenario

Component Fails:Caretaker

Impact:Loss of saved mementos means undo or restore operations fail

Mitigation:Implement persistent storage or backup for mementos to prevent data loss

Architecture Quiz - 3 Questions

Which component is responsible for storing the internal state snapshot without exposing details?

A Originator

B Memento

C Caretaker

D User

Design Principle

The Memento pattern separates state capture and storage from the object itself, preserving encapsulation while enabling undo functionality. It clearly divides responsibilities among Originator (state owner), Memento (state snapshot), and Caretaker (state manager).