DDD for dummies: #sqn #saidnooneever

Before everything, let me explain what “sqn” means… In Brazil, SQN means “Só que não”, that in a poor translation means “But it’s not”, but is a lot more completed than that! It’s something like “no way” in an ironic way.

Going back to DDD, as I said in the last post DDD — a superficial view, it means “Domain Driven Design”.

I started to study it more deeply and I saw how complex and extended it is. It involves many concepts. It became impossible to understand DDD just in theory. (I have this problem at all… I really like to get my hands dirty…). So, I created a project, driven by this great guideline (unfortunately — or fortunately — the class is in Portuguese), and then I created my own guideline and structure.

Above is the structure of DDD.

And bellow is the structure of my understanding of the project.

The project DDD.Demo.AspNetMVC.Products is available at my GitHub account. I used:

• Asp.Net MVC 5 as Presentation Layer
• EntityFramework as the Repository Pattern in the Infrastructure Layer
• Code First: EF Migrations to create/update database
• Fluent API
• AutoMapper to map the View Model Entities to the Domain Entities and vice-versa.
• Ninject MVC5 to the container of MVC’s Dependency Injector
• SQL Server Local as the database

Baby steps:

1- To create the project/solution and the structural folders

2- Domain Layer: To create the domain entities

3- Infrastructure Layer: To build the Context/DbContext/DbSet

4- Presentation Layer: ConnectionString at the MVC Project (WebConfig)

5- In the Infra Layer, create a EntityConfig, that will be the map between the repository and the database.

6- Package Manage Console: Enable Migrations / Update-Database

7- Repositories Interfaces: Base (generic with standard CRUD’s calls) and Specific for each Domain Entity

8- Repositories implementations: Base(generic) and Specific

9- Domain Layer/Services interfaces: Base(generic) and Specific

10- Domain Layer/Services implementation: Base(generic) and Specific, using Dependency Injection of the repository’s interface inside the Constructor

11- Application Layer/Application interfaces: Base and Specifics

12- Application Layer/Application implementation: Base and Specifics (DI of the Service’s interfaces inside the Constructor)

13- Presentation Layer: to create the ViewModels based in the DomainEntities, using the AutoMapper to map both entities.

14- To create the MVC Controllers, and in this case a use of a container (Ninject) is necessary to inject the application’s interfaces.

15- To create the Views

Some points we should keep in mind when using DDD:

• You must keep the persistence ignorance of the domain. Many layers can have the domain as reference, but the domain must not reference any other layer.
• Ensure that the software architecture is designed separately in well-defined layers
• As a SOLID expert, never reference a layer directly. Always use abstractions.

DDD is easier to understand when you start to see a real project being built from the scratch. I hope I could help you! :)

See you in the next post!