C# 获取连接字符串时出错：ArgumentNullException:值不能为null。参数名称：connectionString

我正在使用ASP.NETCore2.0。下面是我的代码

启动：

namespace foo
{
    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)
        {
            // Add framework services.
            services
                .AddMvc()
                .AddJsonOptions(options => options.SerializerSettings.ContractResolver = new DefaultContractResolver());
            services.AddDbContext<fooContext>(options => options.UseSqlServer(Configuration.GetConnectionString("UserDatabase")));
        }

        // 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.UseBrowserLink();
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
            }

            app.UseStaticFiles();

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

{
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Information"
    },
    "ConnectionStrings": {
      "UserDatabase": "Server=DESKTOP-FSES7UK;Database=xxx;User Id=sa; Password=xxxxxxx;Trusted_Connection=True;"
    }
  }
}

---

如何修复它？

问题是您的

连接字符串

对象已成为

日志记录

对象的属性。编写

appsettings.json

，如下所示：

{
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Information"
    },
  },
  "ConnectionStrings": {
      "UserDatabase": "Server=DESKTOP-FSES7UK;Database=xxx;User Id=sa; Password=xxxxxxx;Trusted_Connection=True;"
  }
}

---

如评论中所述，尝试将连接字符串移动到顶部（建议）修复方法是将键*

“ConnectionString”

*置于

日志记录

键之外

appsettings.json

{
  "ConnectionStrings": {
      "UserDatabase": "Server=DESKTOP-FSES7UK;Database=xxx;User Id=sa; Password=xxxxxxx;Trusted_Connection=True;"
  },
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Information"
  }
}

---

尝试在JSON文件的顶部使用ConnectionString。如果它能正常工作，那么您就是专业的。是的@Sajeetharan是对的。您在日志中有您的连接树。在那里找不到它。将连接字符串移到顶层日志之外谢谢，我多次发现错误类型。我会记住的。

尝试将连接字符串移到顶部

——这不是问题！您可以将它放在

appsetings.json

中的任何位置。这不是实际的问题，但我建议将它放在

的顶部或日志键的外部

——这意味着这也不是强制性的！！这是必须的。您不能将

或
与前面的句子放在一起！哈哈！谢谢你纠正它。我希望OP能得到答案：）所以没关系。@Sajeetharan欢迎！但在你多次修改你的答案之前，正确的答案已经发布了