Executing EFcore Migrations inside a .NETStandard Library project

Question

My question is basically: is it possible to use Entity Framework Core (and migrations) inside a .NET Standard 2.0 library project? (not a core project)

I currently have 2 projects:

• ASP.NET Core main project: I don't want anything with databases or EF inside this project, so I added a reference to the .NETstandard2.0 DAL project

• .NETStandard2.0 data access layer project: EF Core with database migrations project for accessing the database. The main project uses this project to get data from the database.

For the .NETStandard DAL project, I use the following settings and classes: the .csproj file contains the dependencies for EF and migrations:

<ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.Identity.EntityFrameworkCore" Version="2.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="2.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="2.0.0" />
</ItemGroup>

<ItemGroup>
    <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.0" />
</ItemGroup>

After calling dotnet restore, I created a DbContext descendant:

class MyTestContext: DbContext
{
    public MyTestContext(DbContextOptions<MyTestContext> options) : base(options)
    {
    }

    public DbSet<Class1> Class1Table { get; set; }
}

And added a DbContextFactory with IDesignTimeDbContextFactory like:

class DbContextFactory : IDesignTimeDbContextFactory<MyTestContext>
{
    public MyTestContext CreateDbContext(string[] args)
    {
        var builder = new DbContextOptionsBuilder<MyTestContext>();
        builder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=efmigrations2017;Trusted_Connection=True;MultipleActiveResultSets=true",
            optionsBuilder => optionsBuilder.MigrationsAssembly(typeof(MyTestContext).GetTypeInfo().Assembly.GetName().Name));

        return new MyTestContext(builder.Options);
    }
}

Okay, so far everything works fine and the .NETStandard project builds successfully.

Now I want to create my first migration by executing:

dotnet ef migrations add InitialCreate

This throws an error:

If I understand the error message correctly, EF Core can only be used in .NET Core and .NET Framework projects and NOT in .NETStandard projects?

If that is true, how can I separate the EF database logic from my other applications?

If not, how can I get the migrations to work?

Thank you in advance

Answer 1

You have two options.

One: Use your ASP.NET Core project as the startup project.

dotnet ef migrations add InitialCreate --startup-project ..\MyWebApplication

Two: Cross-target .NET Core in your class library. (Edit the *.csproj)

<PropertyGroup>
  <!-- Note: This property name becomes plural. -->
  <TargetFrameworks>netcoreapp2.0;netstandard2.0</TargetFrameworks>
</PropertyGroup>