從控制台運行dotnet core應用程序時無法解決依賴關系

Question

我正在使用Dotnet Core Web-api作為后端和Angular2作為前端編寫客戶端-服務器應用程序。 持久層使用EntityFramework Core訪問postgre數據庫。 為了嘗試我的應用程序，我添加了一個數據庫種子類來創建一些可以使用的測試數據。 在這堂課上，我的問題開始了。

當我從Visual Studio Code運行應用程序時，一切工作正常。 如果使用“ dotnet run”從終端啟動應用程序，則會收到以下異常：

Unhandled Exception: System.Exception: Could not resolve a service of type 'OpenGameListApp.Data.DbSeeder' for the parameter 'dbSeeder' of method 'Configure' on type 'OpenGameListApp.Startup'. ---> System.ArgumentNullException: Value cannot be null.
Parameter name: connectionString
   at Microsoft.EntityFrameworkCore.Utilities.Check.NotEmpty(String value, String parameterName)
   at Microsoft.EntityFrameworkCore.NpgsqlDbContextOptionsExtensions.UseNpgsql(DbContextOptionsBuilder optionsBuilder, String connectionString, Action`1 NpgsqlOptionsAction)
   at OpenGameListApp.Startup.<ConfigureServices>b__4_0(DbContextOptionsBuilder options) in /home/noam/projects/dotnet/OpenGameListApp/src/Startup.cs:line 43
   at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.DbContextOptionsFactory[TContext](IServiceProvider applicationServiceProvider, Action`2 optionsAction)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.AspNetCore.Hosting.Internal.ConfigureBuilder.Invoke(Object instance, IApplicationBuilder builder)
   --- End of inner exception stack trace ---
   at Microsoft.AspNetCore.Hosting.Internal.ConfigureBuilder.Invoke(Object instance, IApplicationBuilder builder)
   at Microsoft.AspNetCore.Hosting.ConventionBasedStartup.Configure(IApplicationBuilder app)
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()
   at Microsoft.AspNetCore.Hosting.WebHostBuilder.Build()
   at OpenGameListApp.Program.Main(String[] args) in /home/noam/projects/dotnet/OpenGameListApp/src/Program.cs:line 15

Startup.cs類的代碼：

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services
    services.AddMvc();

    // Add entity framework
    services.AddEntityFrameworkNpgsql()
        .AddDbContext<ApplicationDbContext>(options => 
            options.UseNpgsql(Configuration["Data:DefaultConnection:ConnectionString"]));    

    // Add database seeder
    services.AddSingleton<DbSeeder>();
}

// 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, DbSeeder dbSeeder)
{
    // Add logger
    loggerFactory.AddConsole(Configuration.GetSection("Logging"));
    loggerFactory.AddDebug();

    // Rewrite all routing urls including the root one to the index.html file by adding the following rules
    var rewriteOptions = new RewriteOptions().AddIISUrlRewrite(env.ContentRootFileProvider, "rewrite-rules.xml");

    // Add iis url rewrite features to kestrel            
    // Note: the app.UseRewriter method must be called before app.UseDefaultFiles and app.UseStaticFiles
    app.UseRewriter(rewriteOptions);

    // In order for your Web app to serve a default page without the user having to fully qualify the URI,
    app.UseDefaultFiles();

    // Enable service of static files in wwwroot folder
    app.UseStaticFiles(new StaticFileOptions()
    {
        OnPrepareResponse = (context) => 
        {
            // Disable caching for all static files
            context.Context.Response.Headers["Cache-Control"] = Configuration["StaticFiles:Headers:Cache-Control"];
            context.Context.Response.Headers["Pragma"] = Configuration["StaticFiles:Headers:Pragma"];
            context.Context.Response.Headers["Expires"] = Configuration["StaticFiles:Headers:Expires"];
        }
    });

    // Enable the use of asp.net mvc framework
    app.UseMvc();     

    // Initialize auto mapper
    Mapper.Initialize(cfg => cfg.CreateMap<Item, ItemViewModel>());

    // Seed database
    dbSeeder.SeedIt();               
}

如果我從Startup類中刪除dbSeeder，則該異常消失。 如果有人可以向我指出這里發生的事情，我將不勝感激。

Answer 1

Martin Ullrich的評論為我指明了正確的方向：

似乎無法從配置中讀取連接字符串，因為對UseNpgsql（）的調用引發了

確實無法從配置中讀取連接字符串。 在我的項目中，我有兩個不同的appsettings文件： appsettings.development.json和appsettings.json 。 僅前者包含連接字符串。 當我在Visual Studio Code中運行應用程序時，它將在調試環境中啟動，因此能夠讀取連接字符串。

但是，使用dotnet run從終端運行應用程序似乎可以在生產環境中運行該應用程序。 將終端中使用的環境更改為開發后（ export ASPNETCORE_ENVIRONMENT=Development ），一切正常。