Cannot resolve DbContext in ASP.NET Core 2.0

问题

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?

回答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.

回答2:

Was getting this error while following the official ASP.Net MVC Core tutorial, in the section where you are supposed to add seeded data to your application. Long story short, adding these two lines

 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.DependencyInjection;

to the SeedData class solved it for me:

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using System;
using System.Linq;

namespace MvcMovie.Models
{
public static class SeedData
{
    public static void Initialize(IServiceProvider serviceProvider)
    {
        using (var context = new MvcMovieContext(

           serviceProvider.GetRequiredService<DbContextOptions<MvcMovieContext>>()))
        {
            // Look for any movies.
            if (context.Movie.Any())
            {
                return;   // DB has been seeded
            }
  ...

Can't tell you the WHY, but these were two of the options I got from following the Alt + Enter quick fix option.

回答3:

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

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        var key = Encoding.ASCII.GetBytes(Configuration.GetSection("AppSettings:Token").Value);
        services.AddDbContext<DataContext>(x => x.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")).EnableSensitiveDataLogging());
        services.AddMvc();
        services.AddTransient<Seed>();
        services.AddCors();
        services.AddScoped<IAuthRepository, AuthRepository>();
        services.AddScoped<IUserRepository, UserRepository>();
        services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme).AddJwtBearer(Options =>
            {
                Options.TokenValidationParameters = new TokenValidationParameters
                {
                    ValidateIssuerSigningKey = true,
                    IssuerSigningKey = new SymmetricSecurityKey(key),
                    ValidateIssuer = false,
                    ValidateAudience = false
                };
            }

        );

    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env ,Seed seeder)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler(builder =>
            {
                builder.Run(async context =>
                {
                    context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
                    context.Response.Headers.Add("Access-Control-Allow-Origin", "*");
                    var error = context.Features.Get<IExceptionHandlerFeature>();
                    if (error != null)
                    {
                        context.Response.AddApplicationError(error.Error.Message);
                        await context.Response.WriteAsync(error.Error.Message).ConfigureAwait(false);
                    }
                });
            });
        }
        seeder.SeedUser();
        app.UseCors(x=>x.AllowAnyHeader().AllowAnyMethod().AllowAnyOrigin().AllowCredentials());
        app.UseMvc();
    }
}

}

来源：https://stackoverflow.com/questions/46063945/cannot-resolve-dbcontext-in-asp-net-core-2-0