Question

我全新安装了VS 2016 15.3和Dot Net Core 2.0 SDK

我关注tutorial for Dot Net Core 2.0 Razorpages 并已达到＆＃34;模型＆＃34;步。在那里，我按照指令创建了单个实体和dbcontext，并将连接字符串代码添加到教程中指示的位置。我能说的最好，我的项目与教程完全一样。

当我进入下一步并运行Add-Migration Initial时，我得到一个＆＃34;参数null异常：参数错误表明它找不到配置字符串＆＃34;。本教程没有调用Add-Migration命令的任何参数，也没有就此问题提供任何指导。

如何继续学习本教程。似乎没有办法找到本教程的作者。

我在appsettings中定义的连接字符串是：

"ConnectionStrings": {
  "**MovieContext**": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true"

Startup.cs让DbContext服务正在寻找该连接字符串：

services.AddDbContext<MovieContext>(options =>                
    options.UseSqlServer(Configuration.GetConnectionString("**MovieContext**")));

以下是我尝试运行Add-Migration Initial时的输出：

PM> Add-Migration Initial
Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[0]
      User profile is available. Using 'C:\Users\RRR\AppData\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest.
**System.ArgumentNullException: Value cannot be null.
Parameter name: connectionString**
   at Microsoft.EntityFrameworkCore.Utilities.Check.NotEmpty(String value, String parameterName)
   at Microsoft.EntityFrameworkCore.SqlServerDbContextOptionsExtensions.UseSqlServer(DbContextOptionsBuilder optionsBuilder, String connectionString, Action`1 sqlServerOptionsAction)
   at RazorPagesMovie.Startup.<ConfigureServices>b__4_0(DbContextOptionsBuilder options) in C:\Users\RRR\Source\Repos\RazorPagesMovie\RazorPagesMovie\Startup.cs:line 29
   at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c__DisplayClass0_0`1.<AddDbContext>b__0(IServiceProvider p, DbContextOptionsBuilder b)
   at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.DbContextOptionsFactory[TContext](IServiceProvider applicationServiceProvider, Action`2 optionsAction)
   at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c__DisplayClass5_0`1.<AddCoreServices>b__0(IServiceProvider p)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass22_0.<RealizeService>b__0(ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c__5`1.<AddCoreServices>b__5_1(IServiceProvider p)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitIEnumerable(IEnumerableCallSite enumerableCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass22_0.<RealizeService>b__0(ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetServices[T](IServiceProvider provider)
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.FindContextTypes()
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.FindContextType(String name)
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)
   at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration.<>c__DisplayClass0_1.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Value cannot be null.
Parameter name: connectionString

Answer 1

发现错误 - 阅读困难，视力不佳：错误发生在appsettings.json文件中我错误地添加了连接字符串：

  {
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Warning"
    },
    "ConnectionStrings": {
      "MovieContext": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true"
    }
  }
}

（将其作为Logging的一部分而不是正确版本中的第一级条目：）

{
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Warning"
    }
  },
    "ConnectionStrings": {
      "MovieContext": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true"
    }
}

如何在Razorpages教程中处理null参数Error On Add-Migrations

1 个答案: