asp.net core 2.0 - 值不能为null.参数名称:connectionString

Question

添加迁移时,包管理器控制台中出现以下错误

值不能为空.参数名称:connectionString

这是我的创业公司:

namespace MyProject
{
    public class Startup
    {
        public IConfiguration Configuration { get; set; }
        public Startup(IConfiguration config)
        {
            Configuration = config;
        }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddDbContextPool<AppDbContext>(options =>
                             options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
            services.AddTransient<IDevRepo, DevRepo>();
            services.AddMvc();
            services.AddMemoryCache();
            services.AddSession();
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            app.UseStatusCodePages();
            app.UseStaticFiles();
            app.UseMvcWithDefaultRoute();
            app.Run(async (context) =>
            {
                await context.Response.WriteAsync(Configuration["Message"]);
            });
        }
    }
}

程序类:

public class Program
{
    public static void Main(string[] args)
    {
        BuildWebHost(args).Run();
    }

    public static IWebHost BuildWebHost(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .ConfigureAppConfiguration((context, builder) => builder.SetBasePath(context.HostingEnvironment.ContentRootPath)
                       .AddJsonFile("appsettings.json")
                       .Build())

            .UseStartup<Startup>()
            .Build();
}

appsettings.json:

{
  "Message": "Hello World",
  "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\MSSQLLocalDB;Database=NotMyFault;Trusted_Connection=True;MultipleActiveResultSets=true"
  }
}

有趣的是,如果我运行应用程序,它会显示"Hello World",但是当添加迁移时,它无法找到connectionString.有人可以在这里点灯吗？谢谢.

Answer 1

无法找到connectionstring时发生此问题.

你可能在Startup类中有以下代码:

public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<BenchmarkContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("yourConnectionString name from appsettings.json")));
    }

这些方法解决了您的问题:

1-而不是Configuration.GetConnectionString("yourConnectionString name from appsettings.json")只是把你的连接字符串.

public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<BenchmarkContext>(options =>
  options.UseSqlServer("Data Source=.;Initial Catalog=Benchmark;Persist Security Info=True;User ID=****;Password=****"));
    }

2-如果要使用配置文件,请将这些代码添加到Startup类:

public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }
public IConfiguration Configuration;

public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<BenchmarkContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("TestConnection")));
    }

Appsetting.json文件:

{
  "ConnectionStrings": {
    "TestConnection": "Data Source=.;Initial Catalog=Benchmark;Persist Security Info=True;User ID=****;Password=****"
  }
}

之后,在Package Manager Console中执行'add-migration name'命令

Answer 2

我有同样的问题,但我的解决方案要简单得多.我所做的只是改变appsettings.json的顺序:

{
  "Message": "Hello World",
  "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\MSSQLLocalDB;Database=NotMyFault;Trusted_Connection=True;MultipleActiveResultSets=true"
  }
}

至:

{
   "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\MSSQLLocalDB;Database=NotMyFault;Trusted_Connection=True;MultipleActiveResultSets=true"
  },
  "Message": "Hello World"
}

我怀疑appsettings.json文件中有一个参数序列/顺序.

Answer 3

我在负载测试服务时遇到了这样的问题（我向所有人推荐它）并且有大约 3/1000 个错误的请求，所以我改变了

services.AddDbContextPool<AppDbContext>(options =>
options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

到

string connectionString = Configuration.GetConnectionString("DefaultConnection");
services.AddDbContextPool<AppDbContext>(options =>
options.UseSqlServer(connectionString));

所以它读取连接字符串 1 次并且不会在每个请求上使用 Configuration。现在 100% 的请求都成功了。但它似乎是 .Net Core 中的一个错误

Answer 4

我发现了我自己的问题。

我有一个继承 IDesignTimeDbContextFactory 的 AppDbContextFactory 类。删除这个类可以解决这个问题。