Question

我尝试在控制台.net core 2.0应用程序中使用EF Core 2.0。当我使用IDesignTimeDbContextFactory或覆盖OnConfiguring派生类DbContext的{{1}}方法时，CustomerDbContext在包管理器控制台中成功。但是如果我尝试在asp.net核心应用程序中使用Add-Migration，我会收到消息：

AddDbContext

控制台.net核心应用程序的代码段是：

Unable to create an object of type 'CustomerDbContext'

class Program { static void Main(string[] args) { var services = new ServiceCollection(); IConfigurationRoot config = new ConfigurationBuilder() .SetBasePath(Directory.GetCurrentDirectory()) .AddJsonFile("config.json") //needs Microsoft.Extensions.Configuration.Json .Build(); string conn = config.GetConnectionString("WarehouseConnection"); services .AddDbContext<CustomerDbContext>( options => options.UseSqlServer(config.GetConnectionString("WarehouseConnection"))); var provider = services.BuildServiceProvider(); using(var context = provider.GetService<CustomerDbContext>()) { ... } } }包含连接字符串：

config.json

{ "ConnectionStrings": { "WarehouseConnection": "Server=(localdb)\\mssqllocaldb;Database=WAREHOUSE;Trusted_Connection=True;MultipleActiveResultSets=true" }类是：

CustomerDbContext

为什么这种方法失败的任何想法？

Answer 1

从2.0开始，EF工具检查z-index: 1;方法并使用它来访问应用程序服务（如果它存在）。由于您不需要BuildWebHost()使用BuildWebHost()是正确的做法。

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Answer 2

所以你需要实现IDesignTimeDbContextFactory接口。在项目中添加一个实现此接口的类。

public class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<AppDbContext>
{
    public CustomerDbContext CreateDbContext(string[] args)
    {
        IConfigurationRoot configuration = new ConfigurationBuilder()
            .SetBasePath(Directory.GetCurrentDirectory())
            .AddJsonFile("appsettings.json")
            .Build();

        var builder = new DbContextOptionsBuilder<CustomerDbContext>();
        var connectionString = configuration.GetConnectionString("WarehouseConnection");
        builder.UseSqlServer(connectionString);

        return new CustomerDbContext(builder.Options);
    }
}

有关详细信息，请参阅Cannot make migration. ef core 2.0

添加迁移失败，在控制台核心2.0应用程序

2 个答案: