Definitions

Ports and Adapters Pattern

Kommentar is built using the Ports and Adapters pattern, also known as Hexagonal Architecture. This pattern allows for a clean separation between the core application logic and the external systems it interacts with, such as databases, web servers, and APIs. The architecture is designed to be modular and flexible, making it easy to adapt to different technologies and frameworks.

I won’t go into the deep details of the architecture here but if you’re interested in reading more about it, I recommend reading the book Hexagonal Architecture Explained by Alistair Cockburn and Juan Manuel Garrido de Paz.

But to give you a high-level overview, here’s how the architecture is structured:

• Core: This is the heart of the application, containing the business logic and domain models. It is independent of any external systems and can be tested in isolation.
• Ports: These are the interfaces through which the core interacts with the outside world. They define the operations that can be performed on the core, such as fetching comments or creating new ones. There are two types of ports:
  • Driving Ports: These are the interfaces that the core exposes to the outside world. For example, the HTTP API is a driving port that allows external systems to interact with the core.
  • Driven Ports: These are the interfaces that the core uses to interact with external systems. For example, a database port that allows the core to store and retrieve comments.
• Adapters: These are the implementations of the ports that interact with external systems. For example, there is an adapter for the HTTP API, which allows the core to be accessed via HTTP requests.

Command-Query Responsibility Segregation (CQRS)

Kommentar also follows the Command-Query Responsibility Segregation (CQRS) pattern. This pattern separates read and write operations, allowing for more efficient handling of requests.

Think of it like this:

• Commands: These are operations that change the state of the application, such as creating or modifying a comment. They have side effects.
• Queries: These are operations that retrieve data without changing the state of the application. They are pure and have no side effects.

This separation allows for better scalability and performance, as read and write operations can be optimized independently.

Policies

Kommentar also uses something called Policies to handle some functionality.

Policies can be considered as event handlers that are triggered by certain events in the application.

For example, when a comment is created, a policy can be triggered to send a notification to the commenter or perform some other action.