尝试读取 C# .net 6.0 控制台应用程序中的 ConnectionString 值时，得到 Object 参考 Z37A6259CC0C8DAEFF02 错误

Question

I have a console application(.Net 6.0) with app.config file with following data.

<?xml version="1.0" encoding="utf-8" ?>
 <configuration>
<connectionStrings>
    <add name ="ConnectionKey" connectionString="my connection value" providerName="System.Data.SqlClient"/>
</connectionStrings>

I am trying to read the connection string the following way but I get the error "Object reference not set to an instance of an object."

 cnx = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionKey"].ConnectionString);

Is there something more I have to add? Or is there any other approach to read the connectionString value?

Update:

I have changed the app.config to appsettings.json with following code

{
"ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\MSSQLLocalDB;Database=_CHANGE_ME;Trusted_Connection=True;MultipleActiveResultSets=true",
    "MyConn": "my connection string"
}
  }

Answer 1

You can get the connection string like below:

public class HomeController : Controller
{
    public readonly IConfiguration _configuration;
    public HomeController(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public IActionResult Index()
    {
        string conn = _configuration.GetConnectionString("MyConnection");
        var  cnx = new SqlConnection(conn);
        //do your stuff...
        return View();
    }
} 

appsettings.json:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
      "MyConnection": "your connection string"        //focus here...
    }
}