如何将目标框架正确更改为.NET 4.0

Question

I built an application with target framework .NET 4.6 using MVC 5 and Entity Framework 6 using Visual Studio 2017 on my Windows 7 machine. I'm now being told that I should have built the application to target .NET 4.0 because the production environment only has 4.0 installed. So I changed the target framework to 4.0 but now the application will not build on my machine.

I'm guessing I also need to downgrade MVC and EF. How is the proper way of doing this?

And which versions of MVC and EF should I install?

Do I need to make any manual changes to web.config?

Answer 1

There is no "proper" way, you have 3 options, in my favorite order:

• Update the server/install .net 4.5.
• Start over in a new project and make sure you target version 4.0: you can copy most of your source files. You'll probably get some compiler errors, but usually they are easily fixed. This way you'll have the benifit that the used template matches the framework and packages version(s).
• Re-target the used framework in the project properties and replace the packages which are installed and hope for the best (sometimes you need other packages). Hopefully you used the package manager to install those packages. Maybe the update-packages command helps, but be sure to backup your project first. Some packages become obsolete after time, some are renamed. This is what will cause issues. Also, some of the Methods/API calls will be different, so some rework will be needed.

As for the rest of your questions:

I'm guessing I also need to downgrade MVC and EF. How is the proper way of doing this?

Use the nuget package manager

And which versions of MVC and EF should I install?

The nuget package manager will fix this for you.

Do I need to make any manual changes to web.config?

Sometimes: yes.