我是新的EF核心，我试图让它与我的ASP工作。NET Core项目。
当我尝试配置DbContext使用config中的连接字符串时，我在startup.cs中得到了上述错误。我正在遵循这个教程。
有问题的代码在startup.cs中:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.SpaServices.Webpack;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.EntityFrameworkCore;
using tracV2.models;
using tracV2.data;
namespace tracV2
{
public class Startup
{
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
// Add framework services.
services.AddMvc();
services.AddSingleton<IConfiguration>(Configuration);
string conn = Configuration.GetConnectionString("optimumDB");
services.AddDbContext<tracContext>(options => options.usesqlserver(conn));
}
如果我把UseSqlServer方法直接放到上下文中，它就会被识别出来:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
namespace tracV2.data
{
public class tracContext : DbContext
{
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseSqlServer("myrealconnectionstring");
}
我在网上的所有研究都指向了缺失的参考文献，但我似乎找不到我缺失的是哪一本(见图)。