How to use IDesignTimeDbContextFactory implementation in ASP.NET Core 2.1?

Question

I have ASP.NET Core 1.1 project, which I'm trying to convert to v2.1. I've found IDesignTimeDbContextFactory implementation, but I don't understand where I should create the instance of this factory and how to use it for migrations normal working. Now before create/remove migration I must clean and rebuild solution, because if not, I will get this message: Unable to create an object of type 'MyDbContext'. Add an implementation of 'IDesignTimeDbContextFactory<MyDbContext>' to the project, or see https://go.microsoft.com/fwlink/?linkid=851728 for additional patterns supported at design time. All context data is in separated project. How to use IDesignTimeDbContextFactory implementation or what am I doing wrong?

Answer 1

Add this class to folder where you have your DbContext.

public class MyDbContextFactory : IDesignTimeDbContextFactory<MyDbContext>
    {      

        MyDbContext IDesignTimeDbContextFactory<MyDbContext>.CreateDbContext(string[] args)
        {
            IConfigurationRoot configuration = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("appsettings.json")
                .Build();

            var builder = new DbContextOptionsBuilder<MyDbContext>();
            var connectionString = configuration.GetConnectionString("DefaultConnection");

            builder.UseSqlServer(connectionString);

            return new MyDbContext(builder.Options);
        }
    }