实体框架 7 与 .Net 5 中的现有数据库 MVC 6.

嗨，我在使用实体框架 7 MVC 6 中从现有数据库中提取数据时遇到一些问题。(我已经在这里发布了项目代码(。我已经使用正确的连接字符串设置了appsettings.json：

"Data": {
    "DefaultConnection": {
        "ConnectionString": "Data Source=localhost;Initial Catalog=Demo;Integrated Security=True"
}

我有我的自定义上下文：

public class DatabaseContext : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Customer> Customers { get; set; }
}

两个Poco类：

[Table("Customers")]
public class Customer
{
    [Key]
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Username { get; set; }
    public string Password { get; set; }
    public string EmailAddress { get; set; }
    public DateTime Created { get; set; }
    public DateTime Updated { get; set; }
    public User User { get; set; }
    public bool Active { get; set; }
}
[Table("Users")]
public class User
{
    [Key]
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Username { get; set; }
    public string Password { get; set; }
    public string EmailAddress { get; set; }
    public DateTime Created { get; set; }
    public DateTime Updated { get; set; }
    public bool Active { get; set; }
}

我正在启动中设置服务.cs

public Startup(IHostingEnvironment env)
    {
        // Set up configuration sources.
        var builder = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json")
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);
        if (env.IsDevelopment())
        {
            // For more details on using the user secret store see http://go.microsoft.com/fwlink/?LinkID=532709
            builder.AddUserSecrets();
            // This will push telemetry data through Application Insights pipeline faster, allowing you to view results immediately.
            builder.AddApplicationInsightsSettings(developerMode: true);
        }
        builder.AddEnvironmentVariables();
        Configuration = builder.Build();
    }
    public IConfigurationRoot Configuration { get; set; }
    // 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.AddApplicationInsightsTelemetry(Configuration);
        services.AddEntityFramework()
            .AddSqlServer()
            .AddDbContext<DatabaseContext>(options =>
                options.UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]));
        services.AddIdentity<ApplicationUser, IdentityRole>()
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultTokenProviders();
        services.AddMvc();
        // Add application services.
    }
    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole(Configuration.GetSection("Logging"));
        loggerFactory.AddDebug();
        app.UseApplicationInsightsRequestTelemetry();
        if (env.IsDevelopment())
        {
            app.UseBrowserLink();
            app.UseDeveloperExceptionPage();
            app.UseDatabaseErrorPage();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
            // For more details on creating database during deployment see http://go.microsoft.com/fwlink/?LinkID=615859
            try
            {
                using (var serviceScope = app.ApplicationServices.GetRequiredService<IServiceScopeFactory>()
                    .CreateScope())
                {
                    serviceScope.ServiceProvider.GetService<ApplicationDbContext>()
                         .Database.Migrate();
                }
            }
            catch { }
        }
        app.UseIISPlatformHandler(options => options.AuthenticationDescriptions.Clear());
        app.UseApplicationInsightsExceptionTelemetry();
        app.UseStaticFiles();
        app.UseIdentity();
        // To configure external authentication please see http://go.microsoft.com/fwlink/?LinkID=532715
        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });
    }
    // Entry point for the application.
    public static void Main(string[] args) => WebApplication.Run<Startup>(args);
}

我的用户控制器：

[Route("[controller]")]
public class UsersController : Controller
{
    public DatabaseContext _context { get; set; }
    public UsersController(DatabaseContext context)
    {
        _context = context;
    }
    [Route("[action]")]
    public IActionResult Index()
    {
        using (_context)
        {
            List<User> users = _context.Users.ToList();
        }

        return View();
    }
}

当我导航到用户/索引页面时，我在列表行上不断收到以下错误：

$exception {"对象引用未设置为对象的实例。 System.NullReferenceException

由于某种原因，它不会从数据库中提取信息。我在 Microsoft SQLServer 2014 中创建它。并且用户表中有数据。我是否错过了步骤或我是否尝试以错误的方式访问数据？