.Net Core Migration System.ArgumentNullException：值不能為null

Question

這是我的DbContext

public class DocumentStudioDbContext : DbContext
{
    public DocumentStudioDbContext(DbContextOptions<DocumentStudioDbContext> options) : base(options) { }
    public DbSet<Documents> Documents { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.HasDefaultSchema(schema: Environment.GetEnvironmentVariable(DSCASGlobals.DS_DatabaseSchema));
        base.OnModelCreating(modelBuilder);
    }

    public override int SaveChanges()
    {
        Audit();
        return base.SaveChanges();
    }

    public async Task<int> SaveChangesAsync()
    {
        Audit();
        return await base.SaveChangesAsync();
    }

    private void Audit()
    {
        var entries = ChangeTracker.Entries().Where(x => x.Entity is Documents && (x.State == EntityState.Added || x.State == EntityState.Modified));
        foreach (var entry in entries)
        {
            if (entry.State == EntityState.Added)
            {
                ((Documents)entry.Entity).CreatedOn = DateTime.UtcNow;
            }
        ((Documents)entry.Entity).UpdatedOn = DateTime.UtcNow;
        }
    }
}

當我嘗試運行遷移時，出現此錯誤：

System.ArgumentNullException：值不能為null。 參數名稱： 1 sqlServerOptionsAction) at DocumentStudio.Startup.<>c.<ConfigureServices>b__1_0(DbContextOptionsBuilder options) in C:\\Users\\amosa\\source\\repos\\DotNetCore\\DocumentStudio\\DocumentStudio\\Startup.cs:line 48 at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c__DisplayClass1_0 Microsoft.EntityFrameworkCore.SqlServerDbContextOptionsExtensions.UseSqlServer（DbContextOptionsBuilder optionsBuilder，String connectionString，Action 1 sqlServerOptionsAction) at DocumentStudio.Startup.<>c.<ConfigureServices>b__1_0(DbContextOptionsBuilder options) in C:\\Users\\amosa\\source\\repos\\DotNetCore\\DocumentStudio\\DocumentStudio\\Startup.cs:line 48 at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c__DisplayClass1_0中的Microsoft.EntityFrameworkCore.Utilities.Check.NotEmpty（String value，String parameterName）的connectionString 1 sqlServerOptionsAction) at DocumentStudio.Startup.<>c.<ConfigureServices>b__1_0(DbContextOptionsBuilder options) in C:\\Users\\amosa\\source\\repos\\DotNetCore\\DocumentStudio\\DocumentStudio\\Startup.cs:line 48 at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c__DisplayClass1_0 2.b__0（IServiceProvider p， DbContextOptionsBuilder b）Microsoft.Extensions.D的Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.DbContextOptionsFactory [TContext]（IServiceProvider applicationServiceProvider，Action 2 optionsAction) at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c__DisplayClass10_0 1.b__0（IServiceProvider p）at Microsoft.Extensions.D ependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory（FactoryCallSite factoryCallSite，ServiceProviderEngineScope范圍）在Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite（IServiceCallSite callSite，TArgument參數），Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine。<> c__DisplayClass1_0.b__0（ServiceProviderEngineScope范圍）。 ServiceLookup.ServiceProviderEngine.GetService（類型serviceType，ServiceProviderEngineScope serviceProviderEngineScope）
在Microsoft.Extensions.Dependency.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService（IServiceProvider提供程序，類型serviceType）上的Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService（Type serviceType）at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService [T]（IServiceProvider provider）在Microsoft.Extensions.DependencyInjection.AnityFramework.DependencyInjection.EntityFrameworkServiceCollectionExtensions。<> c__10 1.<AddCoreServices>b__10_1(IServiceProvider p) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor Microsoft.Extens的Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped（ScopedCallSite scopedCallSite，ServiceProviderEngineScope范圍）中的1.<AddCoreServices>b__10_1(IServiceProvider p) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite（IServiceCallSite callSite，TArgument參數） 離開.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitIEnumerable(IEnumerableCallSite enumerableCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor .VisitCallSite（位於Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService的Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine。<> c__DisplayClass1_0.b__0（ServiceProviderEngineScope范圍）中的IServiceCallSite callSite，TArgument參數（類型serviceType，ServiceProviderEngineScope serviceProviderEngineScope）
在Microsoft.Extensions.Dependency.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService（IServiceProvider提供程序，類型serviceType）上的Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService（Type serviceType）at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService [T]（IServiceProvider provider） Microsoft的Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.FindContextTypes（）中的Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetServices [T]（IServiceProvider提供程序），Microsoft的Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.FindContextType（String name）。 Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl（St）中的Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration（String name，String outputDir，String contextType）中的EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext（String contextType） 環名稱，字符串outputDir，String contextType）在Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration。<> c__DisplayClass0_1。<。ctor> b__0（）在Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase。<> c__DisplayClass3_0`1.b__0（ ）在Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute（Action action）值不能為null。 參數名稱：connectionString

我的ConnectionString來自Visual Studio中設置的環境變量。 我不確定如何執行遷移。

我還需要做什么？

編輯：

Startup.cs中的DbContext

services.AddDbContext<DocumentStudioDbContext>(options => options.UseSqlServer(Environment.GetEnvironmentVariable(DSCASGlobals.DS_ConnectionString)));

EDIT2：

管理以從環境變量中獲取變量

Answer 1

  <configuration>

          <connectionStrings>
              <add name="DocumentStudioDb"
                connectionString="Server=(localdb)\mssqllocaldb;Database=DocumentStudioDb;Trusted_Connection=True;" />
                   </connectionStrings>
   </configuration>

/////在您的上下文中編寫此代碼

 protected override void OnConfiguring(DbContextOptionsBuilder   optionsBuilder)
               {
       optionsBuilder.UseSqlServer(ConfigurationManager.ConnectionStrings["DocumentStudioDb"]  .ConnectionString);
                }