Entity Framework Core basically supports .NET Standard 2.0. Therefore, when you write codes for database, we can simply target netstandard2.0 in the .csproj file like below:

<TargetFramework>netstandard2.0</TargetFramework>

On the other hand, it will become a different story when we attempt the code-first approach for database migration using our code. It has to target netcoreapp2.1 in the .csproj like below:

<TargetFramework>netcoreapp2.1</TargetFramework>

Once we setup the project like this, all other projects referencing this has to target netcoreapp2.1; otherwise it won't be compiled. But, are we really sure we should target netcoreapp2.1 for libraries, other than netstandard2.0? As .NET Core is one of the implementations of .NET Standard, unless we're building a end-user applications like web apps or console apps, targeting .NET Standard is the recommended practice and future-proof. In fact, the library containing all database migration details acts as an end-user application. At the same time, it works as a library referenced by other libraries or applications.

In this case, what can we do?

The best practice will be to create a separate project only for database migrations. By doing so, only this migration project targets netcoreapp2.1 and the other project containing DbContext implementation can remain targeting to netstandard2.0. But, you know, life is not that easy. In general, those database migration snapshots and DbContext implementations live together in one project. In this case, we can use multi-targeting. Let's see this:

<TargetFrameworks>netstandard2.0;netcoreapp2.1</TargetFrameworks>

Like above, modify the .csproj file to target both netstandard2.0 and netcoreapp2.1 at the same time. Once it's done, the project is compiled for multi-targeting. Then run the dotnet CLI command like this:

dotnet ef migrations add ThisMigration --framework netcoreapp2.1
dotnet ef database update --framework netcoreapp2.1

Usually the --framework *** option is omitted because the project only has one target framework. But, by adding this option with specific framework, netcoreapp2.1, the database migration can be done with no issue. As well as, this library can be reference by other project targeting .NET Standard.

Easy huh?