.Net Core 2 EF核心连接字符串问题

这是我的 appsettings.json

 "ConnectionStrings": {
    "Circolari": "Server=abcde;Database=Circolari;Trusted_Connection=True;"
  }

这是我的startup.cs

 public Startup(IConfiguration configuration, IHostingEnvironment env)
 {
        Configuration = configuration;
        IConfigurationBuilder configurationBuilder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
        Configuration = configurationBuilder.Build();
 }


 // This method gets called by the runtime. Use this method to add services to the container.

    public void ConfigureServices(IServiceCollection services)
    {
        //Circolari
        string connectoionString = Configuration.GetConnectionString("Circolari");
        services.AddDbContext<CircolariContext>(options => options.UseSqlServer(connectoionString));
        services.AddMvc();
    }

所以当我进行查询时

using (CircolariContext db = new CircolariContext(new DbContextOptions<CircolariContext>()))
{
   List<Argomenti> listaArgomenti = db.Argomenti.ToList();
}

我遇到问题：处理请求时发生未处理的异常。

InvalidOperationException：使用了命名连接字符串，但在应用程序的配置中找不到名称“Circolari”。请注意，仅在使用“IConfiguration”和服务提供程序时才支持命名连接字符串，例如在典型的 ASP.NET Core 应用程序中。看https://go.microsoft.com/fwlink/?linkid=850912 https://go.microsoft.com/fwlink/?linkid=850912了解更多信息。

Microsoft.EntityFrameworkCore.Storage.Internal.NamedConnectionStringResolverBase.ResolveConnectionString（字符串连接字符串）

有人可以帮我吗？

YouContextFile.cs添加此代码

 protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
               // add IConfigurationRoot  to get connection string 
                IConfigurationRoot configuration = new ConfigurationBuilder()
                .SetBasePath(AppDomain.CurrentDomain.BaseDirectory)
                .AddJsonFile("appsettings.json")
                .Build();
                optionsBuilder.UseSqlServer(configuration.GetConnectionString("DefaultConnection"), x => x.UseNetTopologySuite());
            }
        }