C# 找不到类型或命名空间名称“VegaDbContext”

生成项目时出现错误“找不到类型或命名空间名称”VegaDbContext“是否缺少using指令或程序集引用？”。我正在学习使用vs代码编辑器的教程。这是我在创业课上学到的：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.SpaServices.AngularCli;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.EntityFrameworkCore;
using VegaDbContext;

namespace aspcoreangular
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddDbContext<VegaDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("Default")));
            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

            // In production, the Angular files will be served from this directory
            services.AddSpaStaticFiles(configuration =>
            {
                configuration.RootPath = "ClientApp/dist";
            });
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseSpaStaticFiles();

            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller}/{action=Index}/{id?}");
            });

            app.UseSpa(spa =>
            {
                // To learn more about options for serving an Angular SPA from ASP.NET Core,
                // see https://go.microsoft.com/fwlink/?linkid=864501

                spa.Options.SourcePath = "ClientApp";

                if (env.IsDevelopment())
                {
                    spa.UseAngularCliServer(npmScript: "start");
                }
            });
        }
    }
}

这是我的背景：

using Microsoft.EntityFrameworkCore;

namespace aspcoreangular.persistence
{
    public class VegaDbContext : DbContext
    {
        public VegaDbContext(DbContextOptions<VegaDbContext> options) : base(options) 
        { }
    }
}

我还注意到一件事，在vs代码中，如果代码中有错误，我不会得到红线。这就是我没有看到其中错误的原因。你能帮我做这个吗

更换

using VegaDbContext;

与

您在Using指令中引用的是VegaDbContext上下文，而不是它所属的命名空间

进一步阅读

---

非常感谢。我会在10分钟内把这个标记为正确答案。

using aspcoreangular.persistence;