static types cannot be used as type arguments

Question

I am porting from traditional .net mvc application to .netcore.

Original application flow:

OSMSelectController -> OSMDB_Loader.cs -> StatusController

where the connectionstring is read and DAL is initialized.

This connectionstring is coming from static class but when I debug the value is null in here:

WPSGlobalSettings.ToolboxConnString

I have a static class for reading connectionstring from appsettings.

WPSGlobalSettings

public static class WPSGlobalSettings
{
    public static NpgsqlConnectionStringBuilder ToolboxConnString = build_conn_str(ToolboxDatabaseName);

private static NpgsqlConnectionStringBuilder build_conn_str(string dbname)
    {
        string dbSetting = ConfigurationHelper.config.GetSection("ConnectionStrings")["DefaultConnection"];

    ...
    }

}

Controller

public class StatusController : Microsoft.AspNetCore.Mvc.ControllerBase
{
    protected StatusDAL status_dal = new StatusDAL(WPSGlobalSettings.ToolboxConnString);
}

Here it gives type exception, wpsglobalsettings was not initialized and toolboxconnstring is null.

I have tried adding it as singleton to Startup but then i get

static types cannot be used as type arguments

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
     services.AddSingleton<IConfiguration>(Configuration);
        services.AddControllersWithViews();
    services.AddSingleton<WPSGlobalSettings>();
        ConfigurationHelper.Initialize(Configuration);
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        WPSGlobalSettings.Configure(env);
 ...

}

Edit:

I have removed following from Startup.cs

 services.AddSingleton<WPSGlobalSettings>();

Also, introduced DI as follows

protected StatusDAL status_dal;//= new StatusDAL(WPSGlobalSettings.ToolboxConnString);

public StatusController(IConfiguration config)
    {
            status_dal = new StatusDAL(config.GetConnectionString("toolboxConnectionStrWPS"));
    }

Now another problem is older code calls controller constructor from another class as follows:

OSMDB_Loader.cs

public StatusAck LoadOSMSections(OsmLoadRequest request)
    {
        
        StatusAck statusack = new StatusController().PostStatusRecord(); 
    }

Therefore I also added simple constructor in StatusController:

public StatusController()
    {

    }

but now ofcourse status_dal is always null

Something is not quiet right!

You can't pass a static type to a method as a parameter because if you do it would have to be instantiated,If you want to pass connectionstring from appsettings to your controller,just inject IConfiguration into your controller — Ruikai Feng
– Ruikai Feng, Commented Jun 9, 2022 at 6:14

Samra · Accepted Answer · 2022-06-10 03:00:08Z

I got some help here and here Also, the fact that static creates problem with multi-threading..from here

Here is my solution:

Original application flow was

OSMSelectController -> OSMDB_Loader.cs -> StatusController

where the connectionstring was read and DAL was initialized.

Now:

I injected IConfiguration in OSMSelectController and passed it to OSMDB_Loader.cs

private IConfiguration _config;
    public OsmSelectController(IConfiguration config)
    {
        _config = config;
    }

public IActionResult AddRoadsOsm([FromBody]OsmLoadRequest request)
{
...
StatusAck statusack =  new OSM_DBLoader(user_id).LoadOSMSections(request, _config);
        
}

OSMDB_Loader.cs

public StatusAck LoadOSMSections(OsmLoadRequest request, IConfiguration conf)
    {
StatusAck statusack = new StatusController(conf).PostStatusRecord(); //  Issue here is that you need to get the uri
        ...
 }

This way StatusController's correct constructor is hit from where I am able to read the configuration value for connection string

StatusController

protected StatusDAL status_dal;

    public StatusController()
    {
        status_dal = new StatusDAL(WPSGlobalSettings.ToolboxConnString);
    }
    public StatusController(IConfiguration config)
    {
            status_dal = new StatusDAL(config.GetConnectionString("toolboxConnectionStrWPS"));
    }

I would still appreciate if someone can detail how GlobalSettings Static files pose a problem and to cater which we have DependencyInjection and Singleton pattern in .net core.

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