The .NET ecosystem continues to evolve at a remarkable pace. With .NET 11 Preview 6, Microsoft has delivered a host of updates across ASP.NET Core, C#, and the runtime that promise to make developers more productive and applications more secure.

1. ASP.NET Core Upgrades

Async Validation for Minimal APIs

One of the standout features in this preview is the ability to perform asynchronous validation in Minimal APIs. This allows you to validate request data using async operations, such as checking against a database or calling an external service.

app.MapPost("/api/users", async (User user, IUserRepository repo) =>
{
    // Async validation
    if (!await repo.IsEmailUniqueAsync(user.Email))
    {
        return Results.BadRequest("Email already exists");
    }
    
    await repo.CreateUserAsync(user);
    return Results.Created($"/api/users/{user.Id}", user);
});

Automatic Cross-Origin Protection

Security gets a boost with automatic cross-origin protection. The framework now provides better default security headers and protection against common web vulnerabilities.

2. Blazor Enhancements

Virtualization with Scroll-To-Item

Blazor now includes enhanced virtualization capabilities that can scroll directly to a specific item. This is particularly useful for large lists and data grids where you need to navigate to a particular record.

<Virtualize Items="@items" Context="item">
    <ItemContent>
        <div @key="item.Id">@item.Name</div>
    </ItemContent>
    <ScrollToItem @ref="scrollToItem" />
</Virtualize>

@code {
    private Virtualize<Item>? scrollToItem;
    
    private async Task ScrollToItem(int id)
    {
        var index = items.FindIndex(i => i.Id == id);
        await scrollToItem!.ScrollToIndexAsync(index);
    }
}

3. C# Union Types

One of the most anticipated language features is the introduction of union types in C# 15. This feature allows you to define a type that can be one of several different types, making domain modeling more expressive and type-safe.

public union Pet
{
    Dog Dog,
    Cat Cat,
    Bird Bird
}

public class Dog 
{ 
    public string Name { get; set; } 
    public string Breed { get; set; } 
}

public class Cat 
{ 
    public string Name { get; set; } 
    public int LivesRemaining { get; set; } 
}

public class Bird 
{ 
    public string Name { get; set; } 
    public bool CanFly { get; set; } 
}

The compiler enforces exhaustiveness checking, ensuring you handle all cases in your switch statements, eliminating a common source of runtime errors.

4. Runtime and Performance Improvements

• Faster Startup Time: Improved assembly loading and JIT compilation
• Reduced Memory Usage: Optimized garbage collection for server workloads
• Enhanced LINQ Performance: Many LINQ methods now have optimized paths for common scenarios
• Native AOT Improvements: Better support for cross-platform deployments

Getting Started with .NET 11 Preview 6

1. Install the latest .NET 11 SDK from the official Microsoft website
2. Update your existing projects to target net11.0
3. Enable preview features in your .csproj file:

<PropertyGroup>
    <TargetFramework>net11.0</TargetFramework>
    <EnablePreviewFeatures>true</EnablePreviewFeatures>
</PropertyGroup>

Conclusion