Entity framework migrations errors

Question

I want to create a migration for existing entities. I have a DataContext class

public class DataContext : DbContext
{
    public DataContext()
    {
    }
    public DataContext(DbContextOptions<DataContext> options) : base(options)
    {
    }

    public DbSet<AppUser> Users { get; set; }
}

And I added it to the services in IServiceCollection extension method -

public static class DependencyInjection
{
    public static IServiceCollection AddInfrastructure(this IServiceCollection services, IConfiguration configuration)
    {
        services.AddDbContext<DataContext>(options =>
        {
            options.UseSqlServer(configuration.GetConnectionString("DefaultConnection"),
                b => b.MigrationsAssembly(typeof(DataContext).Assembly.FullName));
        });

        return services;
    }
}

When I try to add a migration from Entity Framework command tool - "dotnet ef migrations add InitialCreate" such error occurs:

No database provider has been configured for this DbContext. A provider can be configured by overriding the 'DbContext.OnConfiguring' method or by using 'AddDbContext' on the application service provider. If 'AddDbContext' is used, then also ensure that your DbContext type accepts a DbContextOptions object in its constructor and passes it to the base constructor for DbContext.

Can't really understand what's wrong with my code. It actually works by overriding OnConfiguring method but I need a solution for this kind of approach. Any ideas?

Answer 1

Try to remove the default public constructor (the parameterless one).

When you execute the CLI command you have some additional options like --project and --startup-project. By specifying them it will enable the use of the host builder to create your DB context, and you don't need this parameterless constructor.

The ef cli is using reflection to look into your project and then executes the host builder setup in order to have a service builder. From there it will instantiate the DB context. If it doesn't work. It will fall back first to a design time factory. And finally will use the default constructor (which is happening in this case).