Error Message:
PM> Add-Migration InitialDatabase
dotnet exec needs a managed .dll or .exe extension. The application specified was 'C:\Users\xxxxxx\documents\visual studio 2017\Projects\TheWorld\src\TheWorld\bin\Debug\netcoreapp1.0\TheWorld.runtimeconfig.json'
Process finished with non-zero exit code
PM>
Visual Studio Version: 2017 RC
Project Dependencies :
Error Screenshot :
I had the same problem. The only thing I had to do is changing the Target Framework in the Project properties.
Changing the framework version
I hope this helps.
Shiju Narayan
In VS2017RC - All I had to do was install .NetCore again using Package Manager Console:
Install-Package Microsoft.NETCore.App
Later migration script worked and "dotnet exec needs a managed .dll or .exe extension." error went away.
Tooling for VS and dotnet are still in preview. Try run dotnet ef migrations add InitialDatabase from command line in TheWorld/src folder.
来源：https://stackoverflow.com/questions/41257062/dotnet-exec-needs-a-managed-dll-or-exe-extension-while-adding-entity-framework