There was an error running the selected code generator: Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContextOption

You can create a dbcontext factory class in same folder with your ApplicationDbContext class. This factory class creates ApplicationDbContext at design time and scaffolding runs correctly.

Source: https://github.com/dotnet/Scaffolding/issues/1765

public class ApplicationDbContextFactory : IDesignTimeDbContextFactory<ApplicationDbContext>
{
        public ApplicationDbContext CreateDbContext(string[] args)
        {
            var optionsBuilder = new DbContextOptionsBuilder<ApplicationDbContext>();
            optionsBuilder.UseSqlServer("Server=(localdb)\\MSSQLLocalDB;Database=EcommerceDb;Trusted_Connection=True;MultipleActiveResultSets=true");

            return new ApplicationDbContext(optionsBuilder.Options);
        }
}

After struggling for 3 days, finally I found the mistake and fixed that.

Actually I had to put connection string in MyApp.Persistance.DbContextClass as below

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
                optionsBuilder.UseSqlServer("Data Source=DESKTOP-SV8GPJ2\\SQLEXPRESS;Initial Catalog=StarterAppDB;Persist Security Info=True;User ID=sa;Password=Admin@1234");
            }
        }

Then it worked fine.

In case of .NET 6

Can you try like this

Program.cs

builder.Services.AddDbContext<YourDbContext>(options =>
     options.UseSqlServer("name=ConnectionStrings:DefaultConnection"));

appsettings.json

"ConnectionStrings": {
   "DefaultConnection": "Server=YourServer; Database=YourDb; Integrated Security=true; MultipleActiveResultSets=true; Trusted_Connection=True"
}

YourDbContext.cs

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    if (!optionsBuilder.IsConfigured)
    {
        optionsBuilder.UseSqlServer("Server=YourServer; Database=YourDb; Integrated Security=true; MultipleActiveResultSets=true; Trusted_Connection=True");
    }
}

You need to add the DBContext to service collection in startup.cs file or pass as constructor BGvSystemContext class.

If you don't need the options builder for additional configuration you can dependency inject IConfiguration and use that to pass the connection string inside of OnConfiguring. This will solve the problem with ef code generation.

public class ApplicationDbContext : DbContext
{
    private IConfiguration _config;
    public ApplicationDbContext(IConfiguration config) 
    {
        _config = config;
    }
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(_config.GetConnectionString("DefaultConnection"));
    }
}

And in startup you can use the paramaterless constructor for your db context instead of options builder

You can create a dbcontext factory class in same folder with your ApplicationDbContext class. This factory class creates ApplicationDbContext at design time and scaffolding runs correctly.

public class ApplicationDbContextFactory : IDesignTimeDbContextFactory<ApplicationDbContext>
{
        public ApplicationDbContext CreateDbContext(string[] args)
        {
            var optionsBuilder = new DbContextOptionsBuilder<ApplicationDbContext>();
            optionsBuilder.UseSqlServer("Server=YourServer; Database=YourDb; Integrated Security=true; MultipleActiveResultSets=true; Trusted_Connection=True");

            return new ApplicationDbContext(optionsBuilder.Options);
        }
}