Scaffold Our Shopping Cart Channel (Part I)

Shopping cart

We’ll start developing our shopping cart by writing code that the Channel will use—our functional core. After we build our functional core, we’ll use it to develop a ShoppingCartChannel. We’ll start small and work our way up to a complete cart by the end of this section.

It’s essential to build a functional core that contains logic, data structures, or other parts of a program independent of the user interface. This helps increase the maintainability of our code because the separation between interface and logic means that either can be changed without a complete rewrite of the application. We’ll have an easier time adapting to change and adding new features when our application is split into separate parts this way.

Earlier, our ProductChannel accessed inventory data through an Inventory context—this was our functional core. We’re going to build something very similar in this section—we’ll write a ShoppingCart data structure that holds cart data. We’ll add this code to a Checkout context so that our ShoppingCartChannel can use it without reaching into the context.

Let’s jump into the Checkout context, followed by our ProductController. We’ll build the ShoppingCartChannel in the next lesson.

Build a functional core

When coding a new feature, most people find it helpful to start with the most central part. For us, our entire feature revolves around the concept of a shopping cart, so this is a great place to start writing code. According to our requirements, a shopping cart is a collection of items that can be added to and removed from. Let’s represent this as an Elixir struct.

Create the Checkout.ShoppingCart module and add the following code: