Alejandro Celaya: Properly passing data from outer layers of a PHP application to the use case layer

Alejandro Celaya? has a post to his site sharing some of his experience and advice about how to properly pass data from the outer layers of an app to the "use case" layer. In this situation, the "use case" layer is where most of the processing is happening (versus controllers, views, etc).

Lately, I've been digging a lot in different ways of improving software architecture. Mainly subjects like Clean Architecture, Domain Driven Design, and such.

Those topics cover a lot of advanced and complex practices, but today, I want to talk about a simpler subject. What is the best approach to pass data from outer layers of the application (actions, controllers, async jobs, CLI commands...) to services that are part of the use case layer, by taking advantage of some of the practices promoted by those subjects.

That's a task which is present in any kind of application and is very important to get properly done. You usually need to get data from different origins (a HTTP request, the input of the command line...), filter and validate it, and then use it to perform some kind of task.

He starts off by talking about some of his own previous attempts, starting with a tweet asking where filtering and validation should happen in applications. He then talks about a better approach that makes use of value objects for moving data between service layers. He then walks through a more real-world example (case study) making use of these value objects to handle a user password change.