.Net Core Migration System.ArgumentNullException: Value cannot be null

Question

This is my 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;
        }
    }
}

When I try to run a migration, I get this error:

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, Action1 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_02.b__0(IServiceProvider p, DbContextOptionsBuilder b) at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.DbContextOptionsFactory[TContext](IServiceProvider applicationServiceProvider, Action2 optionsAction) at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c__DisplayClass10_01.b__0(IServiceProvider p) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.b__0(ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.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__101.<AddCoreServices>b__10_1(IServiceProvider p) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitIEnumerable(IEnumerableCallSite enumerableCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.b__0(ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.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.b__0() at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action) Value cannot be null. Parameter name: connectionString

My ConnectionString comes from the Environment Variables that is set in Visual Studio. I am unsure of how I can perform a migration.

What else do I need to do?

EDIT:

DbContext in Startup.cs

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

EDIT2:

Managed to get the variable out from the environment variable

Show your DbContext registration in Statup class and the connection string in appsettings.json file. — TanvirArjel
My connectionstring is stored in the Environment Variables. I don;t use appsettings.json in the project. — JianYA
Okay! Then show how are you getting ConnectionSring in Startup class during DbContext registration. — TanvirArjel
Environment.GetEnvironmentVariable(DSCASGlobals.DS_ConnectionString) is how I get the connection string. I tried setting it to a variable and it works. — JianYA
Environment.GetEnvironmentVariable(DSCASGlobals.DS_ConnectionString) this line is getting ConnectionString null. check it properly please! What is reason behind storing ConnectionString in environment variable instead of appsettings.json file? — TanvirArjel

behzad sayyarpour behzad sayyarpour · Accepted Answer · 2019-06-19T05:07:26

  <configuration>

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

/////write this code in your context

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

.Net Core Migration System.ArgumentNullException: Value cannot be null

1 Answers