Command pattern in LLD - Architecture Diagram

System Overview - Command pattern

The Command pattern is a design approach that turns requests or simple operations into objects. This allows for flexible command execution, queuing, logging, and undo functionality. It helps separate the object that issues a request from the one that knows how to perform it.

Architecture Diagram

User
  |
  v
Invoker
  |
  v
Command Interface <-----> Concrete Command
  |                         |
  v                         v
Receiver <------------------

Components

User

actor

Initiates commands by interacting with the Invoker

Invoker

service

Holds and triggers commands without knowing their implementation

Command Interface

interface

Defines the execute method for commands

Concrete Command

service

Implements the command interface and calls actions on the Receiver

Receiver

service

Performs the actual work when a command is executed

Request Flow - 5 Hops

User → Invoker

Invoker → Concrete Command

Concrete Command → Receiver

Receiver → Invoker

Invoker → User

Failure Scenario

Component Fails:Concrete Command

Impact:Command execution fails, so the requested action is not performed

Mitigation:Invoker can catch errors and notify User or retry; commands can be logged for replay

Architecture Quiz - 3 Questions

Which component is responsible for performing the actual work in the Command pattern?

A Receiver

B Invoker

C Concrete Command

D User

Design Principle

The Command pattern cleanly separates the requester of an action from the object that performs it. This allows commands to be stored, queued, logged, or undone, improving flexibility and decoupling in software design.