升级到 Core 2 Preview 2 后出现“无法解析 .. 类型的服务”

Question

我刚刚升级到 ASP.NET Core 2 Preview 2 并遇到了依赖注入的问题。我得到

运行项目时，无法解析类型为“LC.Tools.API.Startup”的方法“配置”的参数“上下文”的“LC.Tools.API.Data.GenericDbContext”类型的服务。

我用旧版本的时候没有这个问题。

数据库上下文（通用数据库上下文）：

namespace LC.Tools.API.Data
{
    public class GenericDbContext : DbContext
    {
        public GenericDbContext(DbContextOptions<GenericDbContext> options) : base(options) { }

        protected override void OnModelCreating(ModelBuilder builder)
        {
            //Generic
            builder.Entity<Client>();
            builder.Entity<Graphic>();
            .
            .
            .
            .
            .

            //Shop
            builder.Entity<Models.Shop.Store>().ToTable("ShopClient");
            builder.Entity<Models.Shop.Category>().ToTable("ShopCategory");
            .
            .
            .
            .
            .
            .
    }
}

启动.cs：

namespace LC.Tools.API
{
    public class Startup
    {
        public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
                .AddEnvironmentVariables();
            Configuration = builder.Build();

            this.HostingEnvironment = env;
        }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddOptions();
            services.AddDbContext<Data.GenericDbContext>(options => options.UseSqlServer(this.ConnectionString));

            services.AddMvc();
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, Data.GenericDbContext context)
        {
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();

            if (env.IsDevelopment())
            {
                app.UseForwardedHeaders(new ForwardedHeadersOptions
                {
                    ForwardedHeaders = Microsoft.AspNetCore.HttpOverrides.ForwardedHeaders.XForwardedFor,
                    ForwardLimit = 2
                });

                app.UseDeveloperExceptionPage();
                app.UseBrowserLink();
            }

            app.UseStaticFiles();
            app.UseMvc();

            Data.Debug.Init.Initalize(context, env);
        }

        private IHostingEnvironment HostingEnvironment { get; set; }

        public IConfigurationRoot Configuration { get; }

        private string ConnectionString
        {
            get
            {
                return this.HostingEnvironment.IsDevelopment() ? Configuration.GetConnectionString("Development") : Configuration.GetConnectionString("Production");
            }
        }
    }
}

例外：

启动应用程序时发生错误。

InvalidOperationException：无法从根提供程序解析范围服务“LC.Tools.API.Data.GenericDbContext”。

Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteValidator.ValidateResolution(Type serviceType, ServiceProvider serviceProvider) 异常：无法为方法“Configure”的参数“context”解析“LC.Tools.API.Data.GenericDbContext”类型的服务输入“LC.Tools.API.Startup”。

Microsoft.AspNetCore.Hosting.Internal.ConfigureBuilder.Invoke（对象实例，IApplicationBuilder 构建器）

InvalidOperationException: Cannot resolve scoped service
                    'LC.Tools.API.Data.GenericDbContext' from root provider.

Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteValidator.ValidateResolution(Type serviceType, ServiceProvider serviceProvider) Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType) Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider)Microsoft. .Hosting.Internal.ConfigureBuilder.Invoke（对象实例，IApplicationBuilder 构建器）

Answer 1

您正在尝试将上下文注入到Configure不起作用的方法中。从Configure方法中删除注入的上下文，而是注入服务提供者并尝试解析方法中的上下文。

public IServiceProvider ConfigureServices(IServiceCollection services) {
    services.AddOptions();
    services.AddDbContext<Data.GenericDbContext>(options => options.UseSqlServer(this.ConnectionString));

    services.AddMvc();

    // Build the intermediate service provider
    var serviceProvider = services.BuildServiceProvider();
    //return the provider
    return serviceProvider;
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env,
                      ILoggerFactory loggerFactory, IServiceProvider serviceProvider) {
    //...Other code removed for brevity

    var context = serviceProvider.GetService<Data.GenericDbContext>();
    Data.Debug.Init.Initalize(context, env);
}