I'm trying to change ASP.NET Core web application with .NET Framework as a target framework to use .NET Core 3.1.X
I try changing the target framework in the project file (.csproj), I encounter dependency issues, dependency conflict....
Is there any straightforward method to solve this issue?
Before you start your migration, you should know there’s several difference between .net framework and .net core, so please follow the official document to do some Pre-Migration steps.
Then you can follow this official document to migrate your application from framework to .net core 3.1.
Since your ideal .net core version is 3.1, still I suggest you can try to use .net 6. Also, you can use this upgrade tool to reach your goal. In fact, using this upgrade assistant is a batter choice than you doing it by yourself. Even if you are insisting using .net core 3.1, you can use this assistant to upgrade your version to 6 first then change it to 3.1.
Note:
Before you start your migration, please make a backup of your original project. That's because some packages in .net framework may be no longer available in .net core. So if there're some errors occur, you can go back to the original one.
My understanding is that, starting with ASP.NET Core 3.0, .NET Framework is an unsupported target framework, and thus you can only run on the .NET Core runtime.
If this is the case, what NuGet packages can be imported into an ASP.NET Core 3 app?
I assume that you could reference any package that targets netstandard, but what about packages that only target the full framework (i.e., a legacy package that only targets net45)?
What happens if the package you import references an assembly that's not part of .NET Core—i.e., System.Drawing?
TL;DR: You can still reference (packages which depend upon) .NET Framework assemblies from .NET Core 3 and even .NET 5, but you will receive a runtime error if you call into any code which relies upon APIs or libraries not (yet) supported by .NET Core. You can discover these using Microsoft's .NET Portability Analyzer
Background
First off, you're correct that ASP.NET Core 3.x applications can no longer target the .NET Framework, as announced by Microsoft in 2018. That capability previously allowed ASP.NET Core applications to call into .NET Framework libraries, and thus offered an intermediate solution for web applications migrating to .NET Core.
Note: Since the .NET Framework only runs on Windows machines, writing ASP.NET Core web applications which targeted the .NET Framework implicitly restricted those applications to running on Windows.
Behavior
Even when targeting .NET Core or now .NET 5, however, you're still able to reference .NET Framework packages and assemblies, assuming you're on a Windows machine and have the corresponding .NET Framework installed. The inner workings of this are a bit involved, but the short of it is that .NET Core and .NET 5 will evaluate .NET Framework assembles as though they are .NET Standard assemblies. If the API call is also implemented in the .NET Core runtime, it will work fine—but if the API call is exclusively part of .NET Framework, you'll receive an exception.
Surprise! It's really important to emphasize that this is a runtime exception. You will still be able to reference the .NET Framework assembly, write calls to problematic members, and compile your code without any warnings. But as soon as you call into code dependent on a .NET Framework-specific assembly, you'll receive the runtime exception.
Example
With .NET 3.0, a significant portions of .NET Framework libraries have been ported over to .NET Core. In fact, this includes most of the System.Drawing libraries you referenced as an example—though there are good reasons you may not want to use them. If you dig a bit deeper, however, there are plenty of libraries which remain unsupported. One obvious example is the WebConfigurationManager, which could be used to access configuration settings from web.config files.
.NET Framework Code
So, as an example, let's say you have the following function in a .NET Framework class library, which returns an array of keys from your web.config's <AppSetting>s element:
public static class Configuration
{
public static string[] GetAppSettings() => System.Web.Configuration.WebConfigurationManager.AppSettings.AllKeys;
}
ASP.NET Core Code
And then, in an ASP.NET Core controller, you expose an endpoint to retrieve this data:
public class MyController: Controller
{
public IActionResult ApplicationKeys() => Content(String.Join(", ", Configuration.GetAppSettings()));
}
Exception
In an ASP.NET Core 2.x application targeting the .NET Framework, this will work just fine. In an ASP.NET Core 3.x or ASP.NET Core 5 application, however, you'll receive the following runtime error when you call the /My/ApplicationKeys/ route:
System.TypeLoadException: 'Could not load type 'System.Web.Configuration.WebConfigurationManager' from assembly 'System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.'
Avoiding Surprises
If you're anything like me, this will make you incredibly nervous. You'd much rather receive design-time errors—or, at least, compile-time warnings—as soon as you attempt to call into a library relying upon unsupported code. Fortunately, Microsoft offers a .NET Portability Analyzer, which is also available as a Visual Studio Extension, for exactly this purpose.
As of .NET 5, there's also a compatibility analyzer built into the SDK which will identify calls that are not supported by the .NET 5 runtime on particular platforms. This requires that target libraries explicitly annotate their types with the [SupportedOSPlatform()] attribute, so you won't get any warnings for legacy .NET Framework types. But this will help identify similar types of compatibility issues for libraries targeting a variety of platforms.
Example
If you run the Portability Analyzer on the above sample code, for example, it will output an Excel spreadsheet identifying that T:System.Web.Configuration.WebConfigurationManager is Not Supported in e.g. .NET Core,Version=v3.1 or .NET Standard + Platform Extensions,Version=v2.0.
Note: Microsoft used to offer an API Analyzer as a NuGet package, which promised to provide design-time analysis in Visual Studio. Unfortunately, the code hasn't been updated in two years, and the latest release is 0.2.12-alpha. In my evaluation, it was not effective at identifying issues.
Sample Project
I've put together a sample project on GitHub which demonstrates the above behavior. It includes the following projects:
ASP.NET Core 2.0 Website targeting .NET Framework 4.8
ASP.NET Core 3.1 Website targeting .NET Core 3.1
.NET Framework class library with calls to the legacy WebConfigurationManager
Both ASP.NET Core websites include two endpoints which call into the same .NET Framework 4.8 class library. The first is a "Hello world" example which will execute fine on both projects, since it relies exclusively on common APIs:
http://localhost:5000/Basic/Index
The second will fail on the ASP.NET Core 3.1 project, since it calls into the legacy WebConfigurationManager API:
http://localhost:5000/Basic/Configuration
Disclaimer: This is a quick and dirty repository that I put together to verify my understanding prior to posting this. If there's interest, I'll tidy it up and document it. For now, however, it may prove useful for those of you who need to see this in action.
Acknowledgments
#Chris Pratt offered an excellent answer covering similar material last year. It's worth reading.
I have a question about .net Core project.
I have a .Net Core Project referencing other projects.
The problem is that a few projects show the warning saying that "Package 'XXXXX' was restored using .NetFramework, Version=v4.6.1.... instead of targer framework .NetCoreApp".
What kind of problems could I have?
Also can I deploy this in Linux for instance and still working fine?
warning showed
Thanks guys
Look at this thread - For a .Net Core 2.1 project, Why does Nuget restores .Net 4.6.1 packages?
What it basically means is the package you have loaded not suitable for .NET CORE, and was restored using a different version of .Net Framework.
Check if the package exists for .NET CORE (search thru NuGet Manager)
Regarding whether it will work on Linux or not - it depends on the package dependencies (e.g. if it is depending on WinForm for example, it probably won't work on Linux).
Even if it will work, I suggest finding a package suitable for .NET CORE.
i was able to get the sample asp.net embedded powerbi to work with my reports
now i have to migrate it aspnetcore
i was hopeful when i saw this post - seeing that someone was able to get it done
Embed Power BI Report In ASP.Net Core Website
so i:
started a new project with the aspnetcore
installed the powerbi package
now when compiling im getting this warning:
Package 'Microsoft.PowerBI.Api 2.0.11' was restored using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETCoreApp,Version=v2.0'. This package may not be fully compatible with your project.
i searched and couldnt find a powerbi package that was specific to aspnetcore
is there one? will there be a conflict crossing cores? or does it not matter?
UPDATE:
4.6.1 powerbi package does indeed work with aspnetcore 2
but looking forward to a powerbi package specifically coded for core
As you can see this is just a warning, not an error. That warning appears because .NET Core 2.0 applications can use some Nuget packages which target .NET Framework 4.6.1 (or less). However, this inclusion might fail if the referenced .NET 4.x package contains some API not included into .NET Core/.NET Standard 2.0
So, my advice - try to run your application. If it works well at the first glance - then, most probably that PowerBI package does not contain any not supported APIs and will work well further. If it fails right at start - then you will need to wait for the release of the new version of that package which targets .NET Standard 2.0.
I have a project written in VS2012/.Net 4.5 that is essentially a bog-standard, database-first Entity Framework 5 entity model and context, and associated business domain classes. That all works fine when I'm referencing the built assembly from a VS2012/.Net 4.5 application (I've used it successfully with an MVC website and with integration test projects). However when I try to use the exact same assembly from a VS2010/.Net 4 application on the same machine, Visual Studio will add a reference to the assembly with no problem, the classes will also show up under Intellisense (I can add a using statement, for example), but as soon as I try to build the project I get the following error:
Warning 3 The primary reference "MyDotNet45Assembly" could not be resolved because it was built against the ".NETFramework,Version=v4.5" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.0".
My understanding (e.g. from Scott Hanselman here) was that .Net 4.5 was an in-place upgrade to .Net 4.0, so I can't understand why I can't call an assembly created for the newer version. What am I missing or misunderstanding? I can't believe I'm the only person who has hit this issue, but I'm genuinely struggling to find anything on the web that explains what's going on.
I've looked at a number other questions on StackOverflow, none of which seem to quite cover what I'm after, e.g:
Using EF4.0 in a .Net 3.5 app
Using a .Net 4.0 assembly in a .Net 4.5 project