I am getting :
Could not install package 'Npgsql.EntityFrameworkCore.PostgreSQL 2.0.1'. You are trying to install this package into a project that targets '.NETFramework,Version=v4.5.1', but the package does not contain any assembly references or content files that are compatible with that framework.
What am I missing?
If you're looking for Entity Framework Core, then version 2.0.x is only supported for .NET Standard 2.0, which is supported by .NET Framework 4.6.1 and above (or .NET Core).
If you're looking for Entity Framework 6.x, use the package EntityFramework6.Npgsql as suggested above.