How to read connection string in ASP .NET Core Razor Pages

Question

I can't wrap my head around how to retrieve connection strings in ASP .NET Core. I've spent two days trying all the different things and can't get it to work.

I have tried the following methods:

• Using ConfigurationManager.AppSettings a Count returns 0
• Using ConfigurationManager.ConnectionStrings[].ConnectionString - the only connection string that exists is to .\\SQLEXPRESS (have to use index rather than string in the ConnectionStrings[]), specifying a name of the connection results in object reference not set error
• Trying to use WebConfigurationManager can't find how to add it. I've tried System.Web.Configuration, NuGet packages, references.
• Using IConfiguration and dependency injection - I've got no idea how to read the connection string (how to reference the controller in the model and read the value of "xxx" connection string)

ConfigurationManager.ConnectionStrings["SupplierDB"].ConnectionString
// NullReferenceException: Object reference not set to an instance of an object.

ConfigurationManager.ConnectionStrings[0].ConnectionString
// data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true

ConfigurationManager.AppSettings.Count.ToString();
// Returns 0

I've got same connection strings specified in both appsettings.json and web.config. Can someone please point me in the right direction as I'm currently completely lost as nothing works.

appsettings.json

{
  "ConnectionStrings": {
    "CustomerDB": "Data Source=(localdb)\\MSSQLLocalDB;Initial Catalog=Customer_Db;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False",
    "SupplierDB": "Data Source=(localdb)\\MSSQLLocalDB;Initial Catalog=Supplier_Db;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False"
  },
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*"
}

web.config

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <connectionStrings>
    <add name="CustomerDB" providerName="System.Data.SqlClient" connectionString="Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=Customer_Db;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False"/>
    <add name="SupplierDB" providerName="System.Data.SqlClient" connectionString="Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=Supplier_Db;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False"/>
  </connectionStrings>
</configuration>

Answer 1

You can create an AppSettings class like this, by copying your appsettings.json to QuickType :

public class AppSettings
{
    public static ConnectionStrings ConnectionStrings { get; set; }
    public static Logging Logging { get; set; }
    public static string AllowedHosts { get; set; }
}

public class ConnectionStrings
{
    public string CustomerDb { get; set; }
    public string SupplierDb { get; set; }
}

public class Logging
{
    public LogLevel LogLevel { get; set; }
}

public class LogLevel
{
    public string Default { get; set; }
    public string Microsoft { get; set; }
    public string MicrosoftHostingLifetime { get; set; }
}

Then in Startup :

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)
    {
        Configuration.Get<AppSettings>();
        services.AddControllersWithViews();
    }

I use static for easy access instead of injecting AppSettings through DI.

Or if you don't want to put them all in a class, check out the Options pattern from Microsoft.

Answer 2

You could get the connection string value in appsettings.json like below:

For Mvc:

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

    public IActionResult Index()
    {
        string CustomerDBConnectionString = _configuration.GetConnectionString("CustomerDB");
        string SupplierDBConnectionString = _configuration.GetConnectionString("SupplierDB");

        return View();
    }
} 

For Razor Pages:

public class IndexModel : PageModel
{
    public readonly IConfiguration _configuration;
    public IndexModel(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public void OnGet()
    {
        string CustomerDBConnectionString = _configuration.GetConnectionString("CustomerDB");
        string SupplierDBConnectionString = _configuration.GetConnectionString("SupplierDB");
    }
}

Result:

Answer 3

Be sure you have the following NuGets installed:

Microsoft.Extensions.Configuration;
Microsoft.Extensions.Configuration.Json;
//Microsoft.Extensions.Configuration.UserSecrets; //Microsoft.Extensions.Configuration.EnvironmentVariables;

• Generate the following class:

using Microsoft.Extensions.Configuration; using System.IO;

    public static class CustomConfiguration
        {
            public static IConfigurationRoot config;

            public static void BuildConfiguration()
            {
                var builder = new ConfigurationBuilder()
                    .SetBasePath(Directory.GetCurrentDirectory())
                    .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
                    //.AddUserSecrets(Assembly.GetExecutingAssembly(), optional: true, reloadOnChange: true)
                    //.AddEnvironmentVariables();

                config = builder.Build();
            }
}

Then, call the Subject method from anywhere you like

    CustomConfiguration.BuildConfiguration();
    string connectionString = CustomConfiguration.config.GetConnectionString("CustomerDB");