What is Clean Architecture: Part 15-Understanding the Infrastructure and Persistence Layers

When designing applications with Clean Architecture principles, it’s essential to distinguish between the Infrastructure Layer and the Persistence Layer. Both layers play a crucial role in handling the external concerns of your system while keeping the core business logic clean and abstracted.

Let's break down the roles of each layer and how they interact with the overall architecture, with reference to the folder structure from your images.

The Infrastructure Layer

The Infrastructure Layer is responsible for providing implementations for various external services and mechanisms that your application relies on. These services may include file handling, email sending, logging, and third-party API interactions. In Clean Architecture, the core project only defines abstractions (such as interfaces), while the actual implementation details are placed in the infrastructure layer.

Key Components of the Infrastructure Layer :

1. FileExport (CsvExporter.cs):
   • This folder and file handle the logic for exporting data into a CSV file format. This is part of the infrastructure because exporting files is an external operation.

Example:

• The CsvExporter class might implement an interface like IFileExporter defined in the core layer. The core stays unaware of the file format or specifics of the export.

1. Mail (EmailService.cs):
   • The EmailService is responsible for handling email-related operations, such as sending notifications. Again, the core layer would define an interface like IEmailService, and the infrastructure layer implements the actual logic for sending emails (whether using SMTP or an external service like SendGrid).

Example:

• The EmailService implements the interface defined in the core to keep the email-sending logic external to the core business logic.

1. InfrastructureServiceRegistration.cs:
   • This file is likely used to register all the services from the infrastructure layer into the Dependency Injection (DI) container. It ensures that implementations like CsvExporter and EmailService can be injected wherever required throughout the application.

The infrastructure layer ensures that the core logic remains flexible and decoupled from the actual implementations of these external systems. If you need to change how emails are sent or switch to a different file export format, you can do so within the infrastructure layer without affecting the core.

The Persistence Layer

The Persistence Layer is a specialized part of the infrastructure that deals with database access. It is responsible for implementing the database interactions such as querying, saving, and retrieving data. Typically, in a Clean Architecture approach, the core project defines repository interfaces, and the persistence layer provides the concrete implementations using tools like Entity Framework Core.

Key Components of the Persistence Layer (from the images):

1. Configurations:
   • This folder likely contains Entity Framework Core configurations for database entities. These configurations ensure that the database schema aligns with your domain models and handle things like table mappings, relationships, and constraints.

Example:

• Each entity configuration (e.g., EventConfiguration) would be implemented here using the Fluent API to define entity properties and relationships.

1. Migrations:
   • The migrations folder stores EF Core migrations that track changes to your database schema over time. These migrations are used to keep your database schema in sync with your domain models.

Example:

• When adding a new feature, you might generate a migration to update the database schema, and it would be stored in this folder.

1. Repositories:
   • The Repositories folder contains the actual repository implementations. These repositories implement the data access logic defined by repository interfaces in the core layer, such as IAsyncRepository. The persistence layer is where you use Entity Framework Core to interact with the database.

The persistence layer keeps the database concerns separated from the core logic and allows you to swap or upgrade your data access strategy without touching the core business logic. By using Dependency Injection, these repository implementations can be injected wherever needed in the application.

How It All Works Together

• Core Layer: Defines the interfaces and abstractions for business logic and external interactions.
• Infrastructure Layer: Implements services that deal with external systems like files, emails, logging, etc.
• Persistence Layer: Implements data access logic using tools like Entity Framework Core to interact with the database.

At runtime, dependency injection ensures that the concrete implementations from the infrastructure and persistence layers are provided to the core layer's abstractions. This separation of concerns makes the application easier to maintain, test, and extend.

Conclusion

By splitting responsibilities into an infrastructure layer and a persistence layer, we ensure that the core business logic remains clean, decoupled, and adaptable. The Infrastructure Layer handles external services, while the Persistence Layer manages data storage and retrieval. Both layers work together through dependency injection to provide the necessary implementations, keeping the architecture scalable and maintainable.

Comments

[Muhammad Ovais]

A great point often overlooked in Clean Architecture discussions is the importance of managing cross-cutting concerns, such as logging, caching, or error handling. These aspects can be easily scattered across different layers, leading to code duplication and tangling. Implementing these through middleware or aspect-oriented programming (AOP) can ensure they remain centralized, further supporting the architecture’s goal of separation of concerns. This approach not only enhances maintainability but also keeps business logic isolated from technical details, preserving the clean architecture's principles.

[mohamed Tayel]

@ovaismemon
Thank you for pointing that out! I completely agree with the importance of managing cross-cutting concerns like logging, error handling, and maintaining separation of concerns. I'll make sure to cover those topics as I continue this series, along with adding details on implementing logging, error handling, an API layer, and Identity management. Stay tuned for the upcoming articles!