Architecture for Large Scale Apps

In this lesson, you will learn how to structure your Blazor and Razor projects using Clean Architecture to prevent your codebase from becoming an unmanageable "spaghetti" monolith as it scales.

The Problem: Layer Smearing

When building large-scale applications, the most common pitfall is letting UI concerns (Razor/Blazor components) bleed into business logic and data access. If your UserComponent.razor contains direct SQL queries or complex validation logic, changing your database schema will require you to rewrite your UI code. This tight coupling makes testing nearly impossible and scaling a nightmare.

The Solution: Clean Architecture

To keep your app maintainable, we divide the project into distinct layers, each with a single responsibility. Think of these as concentric circles:

1. Domain Layer: The core of your app. It contains your Entities and Interfaces. It has zero dependencies on other layers.
2. Application Layer: Contains your business rules, DTOs, and Service interfaces. It talks to the Domain layer but doesn't care how the UI or Database is implemented.
3. Infrastructure Layer: Handles external concerns like Entity Framework, File Systems, or third-party APIs. It implements the interfaces defined in the Application layer.
4. Presentation Layer (Blazor/Razor): This is purely for rendering. It communicates with the Application layer via Dependency Injection.

Practical Implementation

For example, instead of injecting a DbContext directly into a Blazor page, your page should only know about an interface:

// In the Application Layer
public interface IUserService {
    Task<UserDto> GetUserAsync(int id);
}

// In the Presentation Layer (Blazor)
@inject IUserService UserService

@code {
    private UserDto user;
    protected override async Task OnInitializedAsync() => 
        user = await UserService.GetUserAsync(currentId);
}

By decoupling these layers, you can swap out your database provider, change your UI framework, or update business rules without triggering a cascade of breaking changes across your entire project. The Blazor component only cares about the data contract, not how that data is fetched or stored.

Key Takeaway: By enforcing a dependency flow that points strictly inward toward the Domain, you ensure that your high-level business logic remains protected from changes in your UI or external infrastructure.