实体框架核心-未找到设计时服务

Question

我有一个非常基本的迁移文件。我在Package Manager控制台窗口中执行dotnet ef database update --verbose，但SQL Server中没有生成任何内容。

Package Manager控制台窗口中的最后几行输出如下所示：

Finding design-time services for provider Microsoft.EntityFrameworkCore.SqlServer...
Using design-time services from provider Microsoft.EntityFrameworkCore.SqlServer.
Finding design-time services referenced by assembly BM.Server.
No referenced design-time services were found.
Finding IDesignTimeServices implementations in assembly BM.Server...
No design-time services were found.
Done.

下面是我的代码以及添加和删除迁移的工作。它只是试图更新数据库，我遇到了这个问题。

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<BMDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("BMDbConnectionString")));
    }
}

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

我还为该项目安装了以下nuget包，两个dll都在我的Microsoft.EntityFrameworkCore.Design目录中：

Answer 1

正如在this article中所引用的，您应该添加设计时DbContext。将以下类添加到项目中：

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;

namespace WebApplication8
{
    public class DesignTimeBMDbContext : IDesignTimeDbContextFactory<BMDbContext>
    {
        public BMDbContext CreateDbContext(string[] args)
        {
            var optionsBuilder = new DbContextOptionsBuilder<BMDbContext>();
            // pass your design time connection string here
            optionsBuilder.UseSqlServer("<connection_string>");
            return new BMDbContext(optionsBuilder.Options);
        }
    }
}

添加这个类之后，EF CLI将使用它来创建和更新设计时数据库