Configuration.cs

using GraphQL.EntityFramework;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata;
using Microsoft.Extensions.DependencyInjection;

class Configuration
{
    #region ModelBuilder
    static class ModelBuilder
    {
        public static IModel GetInstance()
        {
            var builder = new DbContextOptionsBuilder();
            builder.UseSqlServer("Fake");
            using var context = new MyDbContext(builder.Options);
            return context.Model;
        }
    }
    #endregion

    void RegisterInContainerExplicit(IServiceCollection serviceCollection)
    {
        #region RegisterInContainer
        EfGraphQLConventions.RegisterInContainer<MyDbContext>(
            serviceCollection,
            model: ModelBuilder.GetInstance());
        #endregion
    }

    public class MyDbContext :
        DbContext
    {
        public MyDbContext(DbContextOptions options) :
            base(options)
        {
        }
    }
}