c# - Entity Framework Core 与 WPF Core - 无法添加迁移

Question

最近我将我的 WPF 应用程序 (.NET 4.7) 迁移到了 .Net Core 3.1。除了我无法生成/添加 EF Core 迁移外，大部分工作正常。

我在以下帖子的帮助下使用依赖注入(inject)集成了我的 dbContext/EF Core:

• https://marcominerva.wordpress.com/2019/03/06/using-net-core-3-0-dependency-injection-and-service-provider-with-wpf/
• https://marcominerva.wordpress.com/2019/03/19/using-entity-framework-core-with-wpf-on-net-core-3-0/

数据库连接正常。但是，当我尝试通过键入以下命令来添加迁移时:Add-Migration InitialMigration 我不断收到以下错误:

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

在 web 应用程序中，这似乎是一个常见/已知的问题，可以通过在程序类中将 CreateHostBuilder 更改为 BuildWebHost 来解决； https://stackoverflow.com/questions/57745481/unable-to-create-an-object-of-type-mycontext-for-the-different-patterns-suppo

我还通过在 options.UseSqlServer 中添加 MigrationsAssembly 找到了一些其他帖子。

长话短说，我尝试了所有这些解决方案，但似乎都不起作用。可能是因为我的应用程序不是 Web 应用程序(没有程序类，例如 BuildWebHost)，而是 WPF(核心)应用程序。

我的 WPF 应用程序初始化代码如下所示:

App.xaml.cs

public partial class App : Application
{
    private readonly IHost host;
    public IServiceProvider ServiceProvider { get; private set; }
    public IConfiguration Configuration { get; private set; }

    public App()
    {
        host = Host.CreateDefaultBuilder()
               .ConfigureServices((context, services) =>
               {
                   ConfigureServices(services);
               }).Build();
    }

    private void ConfigureServices(IServiceCollection services)
    {
        // services for DI...

        services.AddDbContext<MyDbContext>
            (options => 
                options.UseSqlServer(
                        Configuration.GetConnectionString("SqlConnection")));

        services.AddTransient<MainWindow>();
    }

    protected override void OnStartup(StartupEventArgs e)
    {
        var builder = new ConfigurationBuilder()
            .SetBasePath(Directory.GetCurrentDirectory())
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);

        Configuration = builder.Build();

        var serviceCollection = new ServiceCollection();
        ConfigureServices(serviceCollection);

        ServiceProvider = serviceCollection.BuildServiceProvider();

        var mainWindow = ServiceProvider.GetRequiredService<MainWindow>();
        mainWindow.Show();
    }

    protected override async void OnExit(ExitEventArgs e)
    {
        using (host)
        {
            await host.StopAsync(TimeSpan.FromSeconds(5));
        }

        base.OnExit(e);
    }
}

MyDbContext.cs

public class MyDbContext : DbContext
{
    public MyDbContext(DbContextOptions<MyDbContext> options) : base(options)
    {
        Database.Migrate(); 
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Zonnescherm Model
        modelBuilder.Entity<Zonneschermen>().Property(e => e.BreedteZonnescherm).HasColumnType("decimal(17,2)");
        modelBuilder.Entity<Zonneschermen>().Property(e => e.UitvalDoek).HasColumnType("decimal(17,2)");
        modelBuilder.Entity<Zonneschermen>().Property(e => e.ArmLengte).HasColumnType("decimal(17,2)");

        // ScreenRegels Model
        modelBuilder.Entity<ScreenRegels>().Property(e => e.Breedte).HasColumnType("decimal(17,2)");
        modelBuilder.Entity<ScreenRegels>().Property(e => e.Hoogte).HasColumnType("decimal(17,2)");
        modelBuilder.Entity<ScreenRegels>().Property(e => e.DraaistangLengte).HasColumnType("decimal(17,2)");

        // Seed
        modelBuilder.Entity<Instellingen>().HasData(
            // seeding...

        );

        // Seed 
        modelBuilder.Entity<ZonneschermInstellingen>().HasData(
            // seeding...
        );

        // Seed 
        modelBuilder.Entity<ScreenInstellingen>().HasData(
            // seeding...
        );
    }

    public DbSet<Lamellen> Lamellen { get; set; }
    public DbSet<LamellenRegels> LamellenRegels { get; set; }
    public DbSet<Zonneschermen> Zonneschermen { get; set; }
    public DbSet<ZonneschermInstellingen> ZonneschermInstellingen { get; set; }
    public DbSet<Screens> Screens { get; set; }
    public DbSet<ScreenRegels> ScreenRegels { get; set; }
    public DbSet<ScreenInstellingen> ScreenInstellingen { get; set; }
    public DbSet<Instellingen> Instellingen { get; set; }
}

有什么地方出错的线索吗？

Answer 1

对于 .net core 5(不确定它是否适用于早期版本)

只需将此类添加到您的项目中

public class BloggingContextFactory : IDesignTimeDbContextFactory<ApplicationDbContext>
{
    public ApplicationDbContext CreateDbContext(string[] args)
    {
        var optionsBuilder = new DbContextOptionsBuilder<ApplicationDbContext>();
        optionsBuilder.UseSqlServer("your connection string",
                options => options.EnableRetryOnFailure());

        return new ApplicationDbContext(optionsBuilder.Options);
    }
}

文档链接 https://learn.microsoft.com/en-us/ef/core/cli/dbcontext-creation?tabs=dotnet-core-cli#from-a-design-time-factory