c# - Cannot resolve DbContext in ASP.NET Core 2.0

Question

First of all, I'm trying to seed my database with sample data. I have read that this is the way to do it (in Startup.Configure) (please, see ASP.NET Core RC2 Seed Database)

I'm using ASP.NET Core 2.0 with the default options.

As usual, I register my DbContext in ConfigureServices. But after that, in the Startup.Configure method, when I try to resolve it using GetRequiredService, it throws with this message:

System.InvalidOperationException: 'Cannot resolve scoped service 'SGDTP.Infrastructure.Context.SGDTPContext' from root provider.'

My Startup class like this:

public abstract class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<SGDTPContext>(options => options.UseInMemoryDatabase("MyDatabase"))
        services.AddMvc();
    }

    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseMvc();

        SeedDatabase(app);
    }

    private static void SeedDatabase(IApplicationBuilder app)
    {
        using (var context = app.ApplicationServices.GetRequiredService<SGDTPContext>())
        {
            // Seed the Database
            //... 
        }
    }
}

What am I doing wrong? Also, is this the best place to create seed data?

Answer 1

You're registering SGDTPContext as a scoped service and then attempting to access it outside of a scope. To create a scope inside your SeedDatabase method, use the following:

using (var serviceScope = app.ApplicationServices.CreateScope())
{
    var context = serviceScope.ServiceProvider.GetService<SGDTPContext>();

    // Seed the database.
}

Credit to @khellang for pointing out the CreateScope extension method in the comments and to @Tseng's comment and answer re how to implement seeding in EF Core 2.