无法创建 MyDbContext 类型的对象

Question

我正在使用 Autofac 注册 MyDbContext，它工作正常，但是当我尝试使用任何 ef 迁移命令（例如，Add-Migration -Name my-migration）时，我收到错误：

Unable to create an object of type 'MyDbContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

如果我用 IServiceCollection 注册 MyDbContext，错误就会消失。我的 Autofac 配置是：

builder.Register(
    _ =>
    {
        var optionsBuilder = new DbContextOptionsBuilder<MyDbContext>();
        var conn = configuration.GetConnectionString(connName);
        var dbConnection = new NpgsqlConnection(conn);
        var password = configuration.GetPassword(connName);

        dbConnection.ProvidePasswordCallback =
            (host, port, database, username) => password;
        optionsBuilder.UseNpgsql(dbConnection);

        return new MyDbContext(optionsBuilder.Options);
    })
    .AsSelf()
    .InstancePerLifetimeScope();

根据微软文档：

The tools first try to obtain the service provider by invoking Program.CreateHostBuilder(), calling Build(), then accessing the Services property.

我调试了我的应用程序，我能够从通过调用 IHostBuilder.Build() 获得的 IHost 激活 MyDbContext。我缺少什么，我需要做其他事情吗？

提前致谢。

Answer 1

您是否尝试过提到的解决方案

builder.Register(componentContext =>
    {
        var serviceProvider = componentContext.Resolve<IServiceProvider>();
        var configuration = componentContext.Resolve<IConfiguration>();
        var dbContextOptions = new DbContextOptions<TContext>(new Dictionary<Type, IDbContextOptionsExtension>());
        var optionsBuilder = new DbContextOptionsBuilder<TContext>(dbContextOptions)
            .UseApplicationServiceProvider(serviceProvider)
            .UseSqlServer(configuration.GetConnectionString("MyConnectionString"),
                serverOptions => serverOptions.EnableRetryOnFailure(5, TimeSpan.FromSeconds(30), null));

        return optionsBuilder.Options;
    }).As<DbContextOptions<TContext>>()
    .InstancePerLifetimeScope();

builder.Register(context => context.Resolve<DbContextOptions<TContext>>())
    .As<DbContextOptions>()
    .InstancePerLifetimeScope();

builder.RegisterType<TContext>()
    .AsSelf()
    .InstancePerLifetimeScope();

无法创建 MyDbContext 类型的对象

Unable to create an object of type MyDbContext

c#

autofac

entity-framework-migrations