我正在用Adam Freeman的Pro ASP.NET Core MVC 6th Edition做商店应用程序。书中的例子是在Core 1.0中制作的，我使用的是Core 3.0。我在尝试将数据种子到我的数据库(实体框架(时收到如下错误。
System.InvalidOperationException："无法解析作用域内的服务 来自根提供程序的"BookStore.Models.ApplicationDbContext"。
下面是我的代码：
public class SeedData
{
public static void EnsurePopulated(IApplicationBuilder app)
{
ApplicationDbContext context = app.ApplicationServices.GetRequiredService<ApplicationDbContext>();
if (!context.Products.Any())
{
context.Products.AddRange(
new Product {
Name = "Witcher",
Description = "Geralt the Witcher",
Category = "Fantasy",
Price = 30 }
);
context.SaveChanges();
}
}
启动类：
public class Startup
{
public IConfiguration Configuration { get; }
public Startup(IConfiguration configuration, Microsoft.AspNetCore.Hosting.IHostingEnvironment env)
{
Configuration = new ConfigurationBuilder().SetBasePath(env.ContentRootPath).AddJsonFile("appsettings.json").Build();
}
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration["Data:BookStoreProducts:ConnectionString"]));
services.AddTransient<IProductRepository, EFProductRepository>();
services.AddControllersWithViews();
}
public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILoggerFactory loggerFactory, ApplicationDbContext context)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Home/Error");
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Product}/{action=List}/{id?}");
});
SeedData.EnsurePopulated(app);
}
}
和程序.cs
public 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>();
});
}
我在依赖注入方面相当陌生，所以一些解释正在发生的事情会很好。我在网上搜索答案两个多小时，没有任何结果。
以及有关错误的更多信息：
在 Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteValidator.ValidateResolution(Type serviceType， IServiceScope scope， IServiceScope rootScope( at Microsoft.Extensions.DependencyInjection.ServiceProvider.Microsoft.Extensions.DependencyInjection.ServiceLookup.IServiceProviderEngineCallback.OnResolve(Type serviceType， IServiceScope scope( at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType， ServiceProviderEngineScope serviceProviderEngineScope(
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type 服务类型(在 Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider 提供程序，键入服务类型(位于 Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider 提供者(在 BookStore.Models.SeedData.EnsurePopulated(IApplicationBuilder app( in C：\Users\Piotr\source\repos\Store\BookStore\Models\SeedData.cs：line 12 at BookStore.Startup.Configure(IApplicationBuilder app， IWebHostEnvironment env， ILoggerFactory loggerFactory， ApplicationDbContext context( in C：\Users\Piotr\source\repos\Store\BookStore\Startup.cs：line 51 at System.RuntimeMethodHandle.InvokeMethod(Object target， Object[] 参数、签名 sig、布尔构造函数、布尔换行异常( at System.Reflection.RuntimeMethodInfo.Invoke(Object obj， BindingFlags invokeAttr， Binder binder， Object[] parameters， CultureInfo culture(
at Microsoft.AspNetCore.Hosting.ConfigureBuilder.Invoke(Object instance， IApplicationBuilder builder( at Microsoft.AspNetCore.Hosting.ConfigureBuilder.<>c__DisplayClass4_0.b__0(IApplicationBuilder 建造者(在 Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.<>c__DisplayClass13_0.b__2(IApplicationBuilder 应用程序(在 Microsoft.AspNetCore.Mvc.Filters.MiddlewareFilterBuilderStartupFilter.<>c__DisplayClass0_0.g__MiddlewareFilterBuilder|0(IApplicationBuilder 建造者(在 Microsoft.AspNetCore.Server.IIS.Core.IISServerSetupFilter.<>c__DisplayClass2_0.b__0(IApplicationBuilder 应用程序(在 Microsoft.AspNetCore.HostFilteringStartupFilter.<>c__DisplayClass0_0.b__0(IApplicationBuilder 应用程序(在 Microsoft.AspNetCore.Hosting.GenericWebHostService.d__31.MoveNext((
所以解决方案是：
var scopeeee = app.ApplicationServices.CreateScope();
ApplicationDbContext context = scopeeee.ServiceProvider.GetRequiredService<ApplicationDbContext>();
在确保填充方法的开头添加。谢谢！
您需要EnsurePopulated方法中创建作用域，然后从此作用域获取实例。