向项目添加“IDesignTimeDbContextFactory”的实现？

Question

Currently following a course from early 2018.

After running Add-Migration Initial in the Package Manager Console

This is my error message ;

Unable to create an object of type 'AppDbContext'. Add an implementation of 'IDesignTimeDbContextFactory' to the project, or see https://go.microsoft.com/fwlink/?linkid=851728 for additional patterns supported at design time.

The link says to add...

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;
using Microsoft.EntityFrameworkCore.Infrastructure;

namespace MyProject
{
    public class BloggingContextFactory : IDesignTimeDbContextFactory<BloggingContext>
    {
        public BloggingContext CreateDbContext(string[] args)
        {
            var optionsBuilder = new DbContextOptionsBuilder<BloggingContext>();
            optionsBuilder.UseSqlite("Data Source=blog.db");

            return new BloggingContext(optionsBuilder.Options);
        }
    }
}

to my startup.cs...

This is my startup class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using BethanysPieShop.Models;
using Microsoft.Extensions.Configuration;
using Microsoft.EntityFrameworkCore;
using WebApplication5.Models;

namespace BethanysPieShop
{
    public class Startup
    {
        private IConfigurationRoot _configurationRoot;

        public Startup(IHostingEnvironment hostingEnvironment)
        {
            _configurationRoot = new ConfigurationBuilder()
                .SetBasePath(hostingEnvironment.ContentRootPath)
                .AddJsonFile("appsettings.json")
                .Build();
        }

        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit http://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddDbContext<AppDbContext>(options => 
                            options.UseSqlServer(_configurationRoot.GetConnectionString("DefaultConnection")));

            services.AddTransient<ICategoryRepository, CategoryRepository>();
            services.AddTransient<IPieRepository, PieRepository>();

            services.AddMvc();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            app.UseDeveloperExceptionPage();
            app.UseStatusCodePages();
            app.UseStaticFiles();
            app.UseMvcWithDefaultRoute();
        }
    }
}

I'm using Entity Framework Core Tools 2.1.2

AppDbContext.cs

using BethanysPieShop.Models;
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace WebApplication5.Models
{
    public class AppDbContext : DbContext
    {
        public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
        {
        }

        public DbSet<Category> Categories { get; set; }
        public DbSet<Pie> Pies { get; set; }

        public class DbSet
        {
        }
    }
}

Where/location do I implement their code in my code?

What variables do I change?

Answer 1

Try putting this:

services.AddScoped(typeof(IDesignTimeDbContextFactory<BloggingContext>), typeof(BloggingContextFactory));

In Startup.cs, method ConfigureServices, below the services.AddTransient < IPieRepository, PieRepository >();

I hope you find it useful

Answer 2

Last I remember this issue was caused because you're not using the proper WebHostBuilder Method name see this github issue

public class Program
{
    public static void Main(string[] args)
    {
        BuildWebHost(args).Run();
    }

    //.Net-core relies on Duck Typing during migrations and scaffolding
    public static IWebHost BuildWebHost(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>()
            .Build();
}