Command Bus pattern

Laravel Brussels Meetup July 2015

Laravel Brussels Meetup July 2015

Jonathan Van Belle
aka

@Grummfy

Laravel Brussels Meetup July 2015

• What's command bus pattern
  • Advantages
  • "Drawback"
• Alternative to this pattern
• Existing solution
• Demo time

Laravel Brussels Meetup July 2015

What's command bus pattern

Laravel Brussels Meetup July 2015

What's command bus pattern

• Command: message
  • data
• Command Bus: dispatch the message
  • direct, queues, networks, ...
• Handler: use the message to do something
  • save to db
  • log
  • mail
  • ...

Laravel Brussels Meetup July 2015

What's command bus pattern

Bus

Command

Handlers

Bus : handle this command

Laravel Brussels Meetup July 2015

Advantages

• Related to DDD
• Decouple/Reuse code
• Mainly small code
• Controller become testable
• At the end
  • code taste good
  • easier to test
  • easier to refactor

Laravel Brussels Meetup July 2015

Drawback

• Another abstraction layer
• Glue time
  • use DI
• More class
• Need to change habits

Laravel Brussels Meetup July 2015

Alternative to this pattern

• Depending of the context and requirements
• queues
  • interesting to mix it in the command bus
• event
  • Tell something has happened VS needs to happen
  • Have multiple listeners
  • can also be combined

Laravel Brussels Meetup July 2015

Existing solution

• league/tactician
  • xtrasmal\tactician-provider
  • jildertmiedema/laravel-tactician
• simple-bus/message-bus
• Laravel:
  • Command
  • ShouldBeDispatch/ShouldBeQueued
• At the hand, it's convention!
  • Command: interface
  • Command Bus: dispatcher
  • Handlers: interface

Laravel Brussels Meetup July 2015

Existing solution

<?php
class CommandBus
{
  protected $_handlers = array();
  public function __construct($handlers)
  {
    $this->_handlers = $handlers;
  }

  public function handle($command)
  {
    $name = get_class($command);
    if (!isset($this->_handlers[ $name ]))
    {
      throw new UnexpectedException('No handler for the given command ' . $name);
    }

    $this->_handlers[ $name ]->handle($command);
    // only one => use decorator to make onion
  }
}

Laravel Brussels Meetup July 2015

Existing solution

• Can be made at the hand easily
• BUT existing
  • have a lot of plugins
  • have a community
  • is less work to do

Laravel Brussels Meetup July 2015

Example of usage

With decorator (make an onion of handlers)

• log all command
• transact on all query command
• try/catch all command
• valid command
• slack all command
• time mesure
• ...

Laravel Brussels Meetup July 2015

Demo time

Advice

• Use explicit name
• Don't overuse it
• Keep it simple
• Mix it with event and queues
• Think to "do this"
• Try in js too ;)
  • https://github.com/MadeHQ/CommandBus
  • https://gist.github.com/danharper/87269a0628ed97fb026e

Laravel Brussels Meetup July 2015

Resources

• http://php-and-symfony.matthiasnoback.nl/2015/01/some-questions-about-the-command-bus/
• http://laravel.com/docs/5.0/bus
• http://culttt.com/2014/11/10/creating-using-command-bus/
• http://www.reddit.com/r/PHP/comments/29a6qz/what_am_i_missing_with_this_whole_command_bus/cij6avo
• http://shawnmc.cool/command-bus
• Use your favorite web search engine with "command bus php"

Laravel Brussels Meetup July 2015