.NET Core 3.1 - Unable to create an object of type

Question

So, I'm trying to add a migration to the database and it does not work properly.

It gives me this error:

enter image description here

Here's my Startup.cs file:

enter image description here

I tried to add a migration to the database.

PS C:\Users\paulo\Documents\prova-main> dotnet ef --startup-project .\Application\ migrations add MigrationName -c ProvaContext --verbose
Using project 'C:\Users\paulo\Documents\prova-main\Application\Application.csproj'.
Using startup project 'C:\Users\paulo\Documents\prova-main\Application\Application.csproj'.
Writing 'C:\Users\paulo\Documents\prova-main\Application\obj\Application.csproj.EntityFrameworkCore.targets'...
dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=C:\Users\paulo\AppData\Local\Temp\tmp8C9C.tmp /verbosity:quiet /nologo C:\Users\paulo\Documents\prova-main\Application\Application.csproj
Writing 'C:\Users\paulo\Documents\prova-main\Application\obj\Application.csproj.EntityFrameworkCore.targets'...
dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=C:\Users\paulo\AppData\Local\Temp\tmp8F3D.tmp /verbosity:quiet /nologo C:\Users\paulo\Documents\prova-main\Application\Application.csproj
Build started...
dotnet build C:\Users\paulo\Documents\prova-main\Application\Application.csproj /verbosity:quiet /nologo

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:01.31
Build succeeded.
dotnet exec --depsfile C:\Users\paulo\Documents\prova-main\Application\bin\Debug\netcoreapp3.1\Application.deps.json --additionalprobingpath C:\Users\paulo\.nuget\packages --runtimeconfig C:\Users\paulo\Documents\prova-main\Application\bin\Debug\netcoreapp3.1\Application.runtimeconfig.json C:\Users\paulo\.dotnet\tools\.store\dotnet-ef\7.0.1\dotnet-ef\7.0.1\tools\net6.0\any\tools\netcoreapp2.0\any\ef.dll migrations add MigrationName -c ProvaContext --assembly C:\Users\paulo\Documents\prova-main\Application\bin\Debug\netcoreapp3.1\Application.dll --project C:\Users\paulo\Documents\prova-main\Application\Application.csproj --startup-assembly C:\Users\paulo\Documents\prova-main\Application\bin\Debug\netcoreapp3.1\Application.dll --startup-project C:\Users\paulo\Documents\prova-main\Application\Application.csproj --project-dir C:\Users\paulo\Documents\prova-main\Application\ --root-namespace Application --language C# --framework netcoreapp3.1 --working-dir C:\Users\paulo\Documents\prova-main --verbose
Using assembly 'Application'.
Using startup assembly 'Application'.
Using application base 'C:\Users\paulo\Documents\prova-main\Application\bin\Debug\netcoreapp3.1'.
Using working directory 'C:\Users\paulo\Documents\prova-main\Application'.
Using root namespace 'Application'.
Using project directory 'C:\Users\paulo\Documents\prova-main\Application\'.
Remaining arguments: .
Finding DbContext classes...
Finding IDesignTimeDbContextFactory implementations...
Finding application service provider...
Finding Microsoft.Extensions.Hosting service provider...
No static method 'CreateHostBuilder(string[])' was found on class 'Program'.
No application service provider was found.
Finding DbContext classes in the project...
Found DbContext 'ProvaContext'.
Microsoft.EntityFrameworkCore.Design.OperationException: Unable to create an object of type 'ProvaContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728
 ---> System.MissingMethodException: No parameterless constructor defined for type 'Application.Context.ProvaContext'.
   at System.RuntimeType.CreateInstanceDefaultCtorSlow(Boolean publicOnly, Boolean wrapExceptions, Boolean fillCache)
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, Boolean wrapExceptions)
   at System.Activator.CreateInstance(Type type, Boolean nonPublic, Boolean wrapExceptions)
   at System.Activator.CreateInstance(Type type)
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass13_3.<FindContextTypes>b__13()
   --- End of inner exception stack trace ---
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass13_3.<FindContextTypes>b__13()
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func`1 factory)
   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_0.<.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)
Unable to create an object of type 'ProvaContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

Also tried to enter this command inside of the WebAPI directory in the console:

PS C:\Users\paulo\Documents\prova-main\WebApi> dotnet ef migrations add InitialMigration
Build started...
Build succeeded.
System.ArgumentNullException: Value cannot be null. (Parameter 'connectionString')
   at Microsoft.EntityFrameworkCore.Utilities.Check.NotEmpty(String value, String parameterName)
   at Microsoft.EntityFrameworkCore.SqlServerDbContextOptionsExtensions.UseSqlServer(DbContextOptionsBuilder optionsBuilder, String connectionString, Action`1 sqlServerOptionsAction)
   at WebApi.Startup.<ConfigureServices>b__4_0(DbContextOptionsBuilder opts) in C:\Users\paulo\Documents\prova-main\WebApi\Startup.cs:line 23
   at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c__DisplayClass1_0`2.<AddDbContext>b__0(IServiceProvider p, DbContextOptionsBuilder b)
   at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.CreateDbContextOptions[TContext](IServiceProvider applicationServiceProvider, Action`2 optionsAction)
   at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c__DisplayClass10_0`1.<AddCoreServices>b__0(IServiceProvider p)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScopeCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.<RealizeService>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__10`1.<AddCoreServices>b__10_1(IServiceProvider p)   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScopeCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitIEnumerable(IEnumerableCallSite enumerableCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScopeCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScop   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.<RealizeService>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_0.<.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 'connectionString')

Answer 1

Because you have your database context in a separate project. The first thing you should do is define your migration assembly like this:

services.AddDbContext<ProvaContext>(opts => opts.UseSqlServer(Configuration.GetConnectionString("TestApiConnection"), assembly => assembly.MigrationsAssembly(typeof(ProvaContext).Assembly.FullName)));

by default when you open the package manager console default project is set to the main project in your case that is WebApi . just change the default project to Application from the dropdown shown bellow and try again.

if the problem still occurs, change your startup project to Application by right-clicking on it. just for the migration and then change it back to WebApi