无法创建类型为“ MyContext”的对象。针对设计时支持的不同模式 [英] Unable to create an object of type 'MyContext'. For the different patterns supported at design time

问题描述

我在.NET Core上具有ConsoleApplication，并且还向依赖项中添加了DbContext，但是我却遇到了错误：

I have ConsoleApplication on .NET Core and also i added my DbContext to dependencies, but howewer i have an error:

创建一个类型为 MyContext的对象。有关设计时支持的不同模式，请参见 https://go.microsoft.com/fwlink/ ？linkid = 851728

我添加了： var context = host.Services.GetRequiredService< ; MyContext>（）;
另外，我还添加了 private只读DbContextOptions< MyContext> _opts; 在我的Post类中：

i've added: var context = host.Services.GetRequiredService<MyContext>(); Also i've added private readonly DbContextOptions<MyContext> _opts; in my Post Class:

using (MyContext db = new MyContext(_opts))
 {
 db.Posts.Add(postData);
 db.SaveChanges();
 }

我如何添加服务：

.ConfigureServices((context, services) =>
                {
                    services.Configure<DataOptions>(opts =>
                        context.Configuration.GetSection(nameof(DataOptions)).Bind(opts));
                    services.AddDbContext<MyContext>((provider, builder) =>
                        builder.UseSqlite(provider.GetRequiredService<IOptions<DataOptions>>().Value.ConnectionString));

这是我的上下文：

public sealed class MyContext : DbContext
    {
        private readonly DbContextOptions<MyContext> _options;

        public DbSet<PostData> Posts { get; set; }
        public DbSet<VoteData> Votes { get; set; }


        public MyContext(DbContextOptions<MyContext> options) : base(options)
        {
            _options = options;
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
                optionsBuilder.UseSqlite("ConnectionString");
            }
        }

    }

add-migration并出现此错误

I tried add-migration and has this error

我做错了什么？

推荐答案

<我和你有同样的问题。也许不是控制台应用程序，但错误是相同的。因此，我认为值得与我的答案分享。我使用的是 NET Core 3.0 ，并且要解决该问题，必须将 IHostBuilder 更改为 IWebHost ，然后一切都很好。问题出在Program类中。

I've had same problem as You. Maybe it was not for a Console Application but error was the same. So i thought that it is worth to share with my answer. I was using NET Core 3.0 and to fix the problem I have to change the IHostBuilder into IWebHost and then everything was fine. The problem was in class Program.

public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });

进入

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

    public static IWebHost BuildWebHost(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        .UseStartup<Startup>()
        .Build();

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