Unable to create an object of type '[DBContext's Name]'. For the different patterns supported at design time [closed]

I'm following one of Mosh Hamedani Course on ASP.NET MVC in Udemy.

I came across one error while designing my Database using code-first (Entity Framework).

At first, I got the error of " No DbContext was found in assembly". After resolving this problem another one surged from nowhere.

The image below will show you the error found while adding a migration. I've already searched for the same error but in vain. I'm struggling for the past two hours but nothing is solved till now.

Please, someone, help me. Thanks

unable to create an object of type 'Vidly_Context'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

Similar problem after adding own DbContext constructor with (2) parameters. App was ok, but migrations stopped working. Fixed by 1st updating EF (3.1.5 used for strange reason when working with 5) using info from Dotnet tool @xspdf and replacing mentioned constructor by method + hardcoded default connection string if not set.

dotnet tool update --global dotnet-ef

// following command show the most during migration build/run in cmd
// mind current dir is Migrations folder of (VS) startup project here
dotnet ef --startup-project ../ --verbose migrations add test

3.1.5 & context activation Error

The Entity Framework tools version '3.1.5' is older than that of the runtime '5.0.0'. Update the tools for the latest features and bug fixes.
Finding DbContext classes...
Finding IDesignTimeDbContextFactory implementations...
Finding application service provider in assembly '...'...
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 '...Context'.
Microsoft.EntityFrameworkCore.Design.OperationException: Unable to create an object of type '...Context'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728
 ---> System.InvalidOperationException: Unable to resolve service for type 'System.String' while attempting to activate '...'. (my additional parameter)
   at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.ConstructorMatcher.CreateInstance(IServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.CreateInstance(IServiceProvider provider, Type instanceType, Object[] parameters)
   at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetServiceOrCreateInstance(IServiceProvider provider, Type type)
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass13_4.<FindContextTypes>b__13()
   --- End of inner exception stack trace ---
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass13_4.<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, String namespace)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType, String namespace)
   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 '...Context'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

1- Make sure to set your web project as Set as Startup Project

2- In Package Manager Console, set your data access layer (if any) as a default project

3- Then run the command again

The error message states that the context could not be created at design time. If you specify in the migration command the startup project with the --startup-project flag (or -s) you can help the command create the context instance at design time in a similar way to how it would be created at run time.

For example:

cd ./project_with_migrations_folder
dotnet ef --startup-project ../my_startup_project_path/ migrations add myMigration01

I ran into the same issue. OP mentioned they needed to add code to their Startup.cs.

On https://go.microsoft.com/fwlink/?linkid=851728 there's the following code sample;

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
        => services.AddDbContext<ApplicationDbContext>();
}

My code was missing the following in my ConfigureServices method;

services.AddDbContext<ApplicationDbContext>();

After adding this for my database context the issue was resolved.

I ran into this issue when using EF Core code-first migrations in a .NET Core 3 solution that contained both an MVC project and a Blazor project.

If I have the solution's startup project set to the Blazor project I get the error when using add-migration, but I don't if I have the startup project set to the MVC project.

From reading the documentation page linked to by the error message and comparing the code in the startup.cs files for both projects I'm not sure why that would be, but temporarily switching the startup project to the MVC project fixes it for me.