Entity Framework 核心添加迁移给出的值不能为空。 （参数'connectionString'）

Question

我是 .NET Core 的新手，正在使用 Udemy class。我正在尝试启用迁移以执行代码优先，但我一直收到错误

Value cannot be null. (Parameter 'connectionString')

我做了一些研究，似乎大部分时间都是 appsetttings.json 文件中 ConnectionStrings 的拼写错误。但是，我查看了我的所有内容并尝试了几次 copy/paste 以确保我的拼写正确。要么是其他原因，要么是我看了这么多我忽略了一些东西。

Appsettings.json

{
    "ConnectionStings": {
        "DbConnection": "Server=DAVIDPC\SQLEXPRESS01;Database=dotnet-rpg;Trusted_Connection=true;MultipleActiveResultSets=true;"
    },
    "Logging": {
        "LogLevel": {
            "Default": "Information",
            "Microsoft": "Warning",
            "Microsoft.Hosting.Lifetime": "Information"
        }
    },
    "AllowedHosts": "*"
}

Startup.cs

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<DataContext>(x => x.UseSqlServer(Configuration.GetConnectionString("DbConnection")));
    services.AddControllers();
    services.AddAutoMapper(typeof(Startup));
    services.AddScoped<ICharacterService, CharacterService>();
}

Answer 1

应用设置和配置服务方法看起来不错。 试试这个

  "ConnectionStrings": {
    "DbContext": "Data Source=(LocalDb)\MSSQLLocalDB;Initial Catalog=dotnet-rpg;Integrated Security=SSPI; MultipleActiveResultSets=true;",
    "Logging": {
      "LogLevel": {
        "Default": "Information",
        "Microsoft": "Warning",
        "Microsoft.Hosting.Lifetime": "Information"
      }
    }
  }

区别在于连接字符串没有"Data Source"

在配置服务中

services.AddDbContextPool<DataContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("DbContext"))
            );

如果这解决了您的问题，请告诉我。

下面两个参考 link 有实现细节。

Implement create, read, update, and delete functionalities using Entity Framework Core

Configure Azure SQL relational database using vs 2019

Answer 2

在您的示例中，您拼错了 ConnectionStrings

 {
        "ConnectionStrings": {
            "DbConnection": "Server=DAVIDPC\SQLEXPRESS01;Database=dotnet-rpg;Trusted_Connection=true;MultipleActiveResultSets=true;"
        },
        "Logging": {
            "LogLevel": {
                "Default": "Information",
                "Microsoft": "Warning",
                "Microsoft.Hosting.Lifetime": "Information"
            }
        },
        "AllowedHosts": "*"
    }