Scaffolding Entity Framework Controllers with Lamar

Question

I have Lamar set up in my .NET Core 2 project:

    public class Program
    {
        public static void Main(string[] args)
        {
            IWebHost webhost = CreateWebHostBuilder(args).Build();
            //((Container)webhost.Services).GetInstance<IStart>().Run();
            webhost.Run();
        }

        public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                .UseLamar()
                .UseStartup<Startup>();
    }

...

    public class Startup
    {
    ...
        public void ConfigureContainer(ServiceRegistry services)
        {
            services.Configure<Configuration.Auth>("auth", Configuration);
            ...
            services.Scan(s =>
            {
                s.TheCallingAssembly();
                s.WithDefaultConventions();
            });
            services.AddCors();
            services.AddMvc()
                .AddJsonOptions(o =>
                {
                    o.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();
                    o.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
                })
                .SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
            services.AddDbContext<Context>(options => options.UseSqlServer(Configuration.GetConnectionString("defaultConnection")));
        }
    }

However, when attempting to use Scaffold API Controller with actions, using Entity Framework I run into the following error:

There was an error running the selected code generator: 'No parameterless constructor defined for this object.'

Looking up this https://learn.microsoft.com/en-us/aspnet/core/migration/1x-to-2x/?view=aspnetcore-2.2#update-main-method-in-programcs suggested that this can show up in ASP.NET Core 2 projects that attempt to still use the .NET 1.x structure.

I found a hacky work-around that I'll post below, which suggests that the scaffolding code generation may have an issue with Lamar. However, is there a better solution? Can you set up Lamar to be able to handle Entity Framework Code generation?

score 0 · Answer 1 · answered Jan 11 '19 at 04:26

Considering EF was failing in the generate code section, I wondered if perhaps the issue was not the parameterless constructor (I'm pretty sure that whatever unnamed object it was referring to actually has one) but the issue with how the WebHost gets built when using Lamar.

The note in the Lamar documentation on integrating with ASP.NET Core states

Note! The Startup.ConfigureServices(ServiceRegistry) convention does not work as of ASP.Net Core 2.1. Use ConfigureContainer(ServiceRegistry) instead.

I was using that Lamar function in my Startup; however, if I changed it back to ConfigureContainer(IServiceCollection services) (and commented out the Lamar-specific functions, such as Scan), I found that I was able to scaffold the EF controller again.

So, at the moment, my workaround is to comment out Lamar before scaffolding, and then uncomment it back once I'm done. I suspect there may be a better solution though...

Scaffolding Entity Framework Controllers with Lamar

1 Answers1