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Upgrading to ASP.NET Core Version 3.0: Top Tips

So you got excited about ASP.NET Core and started building an application in ASP.NET Core 2.0, 2.1, or 2.2. Now you're wondering how much work is involved in migrating that application to Version 3.0 which came out in late September.

If you've got a vanilla application the answer is ... it's not that painful. For example, to upgrade to Version 3.0, you just need to go into your csproj file and strip out almost everything to leave this:


And I do mean "almost everything." For example, any Package Reference elements that you have that reference Microsoft.AspNetCore packages can probably be deleted.

In ConfigureServices, you'll replace AddMvc with one or more of these method calls, depending on what technologies your application uses:

  • AddRazorPages: If you're using Razor Pages
  • AddControllers: If you're using Web services but not Views
  • AddControllersWithView: If you're using Controllers and Views. This also supports Web services so don't use it with AddControllers

In the Startup.cs file's Configure method, you'll change the IHostingEvnvironment parameter to IWebHostingEnvironment. Inside the method, you'll replace your call to UseMvc with:

  • UseAuthorization and UseAuthorization: Assuming that you're using authentication, of course
  • UseCors: If you want to support Cross-Origin Requests
  • UseEndPoints

With UseMvc gone, you'll need to move any routes you specified in that method into UseEndPoints. That will look something like this:

app.UseEndpoints(endpoints =>
      endpoints.MapControllerRoute("default", "{controller=Home}/{action=Index}/{id?}");

Those changes are all pretty benign because they all happen in one file. The other big change you'll probably have to make (especially if you've created a Web service) is more annoying: NewtonSoft.Json is no longer part of the base package. If you've been using NewtonSoft's JSON functionality, you can (if you're lucky) just switch to the System.Text.Json namespace. If you're unlucky, you'll have some code to track down and rewrite throughout your application.

Sorry about that.

There's more, of course, and there's a full guide from Microsoft. If you've got a relatively straightforward site, though, these changes may be all you need to do.

Posted by Peter Vogel on 10/14/2019 at 2:48 PM

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