In our previous article, we laid the groundwork by creating the Domain Project, setting the stage for a clean and maintainable architecture. Now, it's time to tackle the next big piece of the puzzle: the Application Project. This is where the rubber meets the road, as we begin to structure the core of our architecture. Fasten your seatbelts—this journey will involve several key concepts that are critical to achieving a loosely coupled, scalable application.
The Role of the Application Project
The Application Project is a fundamental part of our architecture's core. If you've been following along, you already know that our architecture is built on the principles of clean architecture. The Application Project is where we implement the core business logic while keeping the code decoupled from the infrastructure. This ensures that our application remains flexible and easy to maintain as it grows.
In our architectural schema, the Application Project is clearly highlighted as part of the core. It's where we handle the flow of data and the execution of business rules, but without direct dependencies on the infrastructure or UI layers. This separation is key to achieving the clean architecture we’re striving for.
Key Concepts: Contracts and Messaging
To maintain this separation and achieve loose coupling, we rely heavily on two concepts: contracts (interfaces) and messaging.
Contracts (Interfaces)
Contracts, or interfaces, are the backbone of our Application Project. They allow us to define the operations and services that our application will rely on, without tying those definitions to specific implementations. This abstraction is critical for maintaining flexibility and enabling easy swapping of implementations when needed.
In our Application Project, you’ll notice that we create a large number of interfaces. This is intentional and essential for building a robust architecture. Most of these interfaces will eventually be implemented in the infrastructure layer, allowing the application core to remain independent and implementation-agnostic.
Messaging
The second concept we’ll leverage is messaging. This allows different components of our application to communicate without direct references to each other. Instead, communication happens through an intermediate or mediator, which facilitates the interaction. This pattern further enforces loose coupling by ensuring that components remain isolated and only interact through well-defined channels.
Implementing the Repository Pattern
One of the first areas where we’ll see the power of contracts in action is in the repository pattern. In our application architecture, the repository pattern serves as a mediator between the application code and the data access layer.
Why Use the Repository Pattern?
The repository pattern creates a layer of abstraction between the business logic and the data access code. This is a common and effective way to ensure that your application code is not cluttered with data access details. Instead, all data access operations are channeled through repositories, which adhere to the DRY (Don’t Repeat Yourself) principle by centralizing these operations.
The Debate: Repository vs. Entity Framework Core
There is some debate around the necessity of using a repository pattern when working with Entity Framework Core, as EF Core’s DbContext already provides many repository-like functionalities. However, I believe that using repositories still holds value, especially in maintaining a clean separation between your application logic and data access code. This is why repositories are included in our architecture.
That said, I’ve decided not to implement a manual unit of work pattern, as EF Core’s DbContext handles this sufficiently. This decision aligns with the philosophy of not reinventing the wheel and focusing on what truly adds value to the architecture.
Creating a Generic Repository
In the demo that follows, we’ll start by creating a generic repository. This will include basic methods like Add, Remove, and GetByIdAsync. However, it’s important to note that at this stage, we are only defining the contracts—not the implementations. The actual implementation of these repositories will be handled later, likely in the infrastructure layer.
Specific Repositories
In addition to a generic repository, there will be situations where we need more specialized repositories. These specific repositories will cater to unique data access needs that aren’t covered by the generic repository. For example, we might need a repository with a method to retrieve all ticket sales for a particular month—something that isn’t generic but is essential for certain business operations.
Conclusion
Designing the Application Project is a crucial step in building a clean, maintainable architecture. By relying on contracts and messaging, we ensure that our application core remains loosely coupled and independent from the implementation details of the infrastructure. The repository pattern further enforces this separation, providing a clean interface for data access operations.
In the next article, we’ll delve deeper into implementing these concepts and bringing our Application Project to life. Stay tuned as we continue building our clean architecture!
For the complete source code, you can visit the GitHub repository: https://github.com/mohamedtayel1980/clean-architecture
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