Asp.net mvc mvc 6 ef7客户表对象在AppDbContext中为空-数据库中有数据

当我输入URL localhost:xxx/api/Customers时，它显示为“is null”。我在调试器模式下查看变量，它显示表customers对象为null

记住表中有数据。有什么想法吗

客户类别

public class Customer
{
    public string Id { get; set; }
    public string lName { get; set; }
}

appsettings.json

{
"Data": {
"DefaultConnection": {
  "ConnectionString": "Server=.\\sqlexpress;Database=EF7;Trusted_Connection=True;"
}
}

AppDbContext

public class AppDbContext : DbContext
{
    public DbSet<Customer> Customers;
    protected override void OnModelCreating(ModelBuilder Builder)
    {
        Builder.Entity<Customer>().HasKey(c => c.Id);
        base.OnModelCreating(Builder);
    }
 }

Startup.cs

public class Startup
{
    IConfigurationRoot Configuration;
    public Startup(IHostingEnvironment env)
    {
        var Builder = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json")
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
            .AddEnvironmentVariables();
        Configuration = Builder.Build();
    }
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc();
        services.AddEntityFramework().AddSqlServer().AddDbContext<AppDbContext>(o=>o.UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]));
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app)
    {
        app.UseIISPlatformHandler();
        app.UseMvc();
    }

    // Entry point for the application.
    public static void Main(string[] args) => WebApplication.Run<Startup>(args);
}

公共类启动
{
i配置根配置；
公共启动（IHostingEnvironment环境）
{
var Builder=new ConfigurationBuilder（）
.AddJsonFile（“appsettings.json”）
.AddJsonFile（$“appsettings.{env.EnvironmentName}.json”，可选：true）
.AddenEnvironmentVariables（）；
Configuration=Builder.Build（）；
}
public void配置服务（IServiceCollection服务）
{
services.AddMvc（）；
services.AddEntityFramework（）；
}
//此方法由运行时调用。请使用此方法配置HTTP请求管道。
公共void配置（IApplicationBuilder应用程序）
{
app.UseIISPlatformHandler（）；
app.UseMvc（）；
}
//应用程序的入口点。
publicstaticvoidmain（字符串[]args）=>WebApplication.Run（args）；
}

没关系，我的数据库集是一个字段而不是属性。所以我刚改为DbSet Customer{get；set}

public class Startup
{
    IConfigurationRoot Configuration;
    public Startup(IHostingEnvironment env)
    {
        var Builder = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json")
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
            .AddEnvironmentVariables();
        Configuration = Builder.Build();
    }
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc();
        services.AddEntityFramework().AddSqlServer().AddDbContext<AppDbContext>(o=>o.UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]));
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app)
    {
        app.UseIISPlatformHandler();
        app.UseMvc();
    }

    // Entry point for the application.
    public static void Main(string[] args) => WebApplication.Run<Startup>(args);
}