As our applications grow in size and functionality, it can become harder and harder to figure out what functionality belongs in what location. Most web applications use the CRUD (Create Read Update Delete) pattern in how it organizes accessing the application's data. In many cases, this encourages our controller objects to get larger and larger, making maintenance and testing more difficult. The required dependencies increase in size, and the scope and it get harder to debug when things go wrong.

The Command Query Responsibility Segregation (CQRS) pattern is a different way of organizing how your application interacts with it's data and helps you keep your reads away from your writes.

In this talk Chris shows how he took a tangled mess of a PHP application that has been in use for more than a decade and used CQRS to make sense of it all.