DDDForum.com is the application that we build in solidbook.io - The Software Design and Architecture Handbook.
Note: It's currently deployed on free tier Heroku, which has some undesirable side-effects like shutting off the server during periods of inactivity. So if it's down for you, refresh a couple of times. Thinking about migrating this to a serverless architecture later on.
- Sequelize - The ORM for Node.js
- Express.js - Lightweight webserver
- Redis - For holding onto JWT tokens and refresh tokens
There's obviously a lot that went into building this from front to back.
The Clean Architecture is a way to reason about where different types of application logic belongs.
There's a lot more to learn about the clean architecture, but for now- just know that it's a way to really separate the concerns of everything that goes into building complex enterprise applications. You'll never see any
infrastructure-related code alongside
domain layer code.
The clean architecture, when combined with Domain-Driven Design, is very powerful :)
In DDD, we build applications on top of a number of subdomains.
A subdomain is a cohesive unit of code that represents exactly one core concept and is responsible for a specific set of concerns in an application architecture. For example, every appliciation has a
userssubdomain. That's responsible for users, identity & access management, authentication, authorization, etc. Sometimes you don't want to build that yourself. Sometimes you can go with an off-the-shelf solution like Auth0. But there are subdomains in your application that you cannot simply outsource. These are the family jewels; the thing that's actually novel about your app. This is the subdomain that no one (except you) can code. Know why? Because only you have the domain knowledge to build it exactly the way that it should be built. You understand the domain.
In DDDForum, we have 2 subdomains: The
users subdomain and the
Each subdomain has a:
domainlayer: where the highest-level policy, domain objects, and domain rules belong (
applicationlayer: where the use cases / features that utilize domain objects belong (
adapterlayer: where we define abstractions so that
applicationlayer code can interact with
infrastructurelayer concepts, without actually requiring on
infrastructure(because that would break the dependency rule). Here we write things like
IUserRepo- repository adapter,
IJWTTokenService- an abstraction of a cache (redis) that manages tokens, etc.
infrastructurelayer: where we create concrete implementations of the abstractions from the
adapterlayer so that they can be spun up at runtime thanks to the power of polymorhpism :) (more on this later).
If you haven't already, I recommend you read this article on use cases and subdomains.
Let's identify some of the actual concepts that exist in each subdomain.
users subdomain, we're only concerned with concepts that are related to authentication, roles, etc. Here are a few examples of classes and concepts that exist at each layer.
IUserRepo(respository interface adapter)
SequelizeUserRepo(a concrete implementation of the IUserRepo),
UserDTO(data transmission objects).
forum subdomain, we're only concerned with concepts that have to do with building a forum. You won't see any domain concepts from the
forum. In the
forum subdomain, the concept most equivalent to a
user, is a
Here are a few examples of concepts from the
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