System.Configuration.ConnectionStringSettingsCollection.this[string].get returned null on ASP.Net Core

Question

I get an error of Object reference not set to an instance of an object when I try to retrieve my data from a database. I know that EF has a dbcontext that I can use, but I want to try this approach as my colleagues use this kind. I can get the ConnectionString fine, I see it in my breakpoint, but after that line, I get the error:

System.Configuration.ConnectionStringSettingsCollection.this[string].get returned null

My code is below:

appsettings.json

"AllowedHosts": "*",
  "ConnectionStrings": {
    "DefaultConnection": "Server=DESKTOP-MIHT9TM\\SQLEXPRESS;Database=react_db;User=sa;Password=OtlPHP07"
  }

Startup.cs

public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();

            services
                .AddMvc(options =>
                {
                    options.EnableEndpointRouting = false;
                })
                .AddNewtonsoftJson()
                .SetCompatibilityVersion(CompatibilityVersion.Version_3_0)
                .AddJsonOptions(options =>
                {
                    options.JsonSerializerOptions.IgnoreNullValues = true;
                    options.JsonSerializerOptions.WriteIndented = true;
                });

            services.AddSingleton<IConfiguration>(Configuration);
        }

DepartmentController.cs

[Route("api/[controller]")]
    [ApiController]
    public class DepartmentController : ControllerBase
    {
        private readonly IConfiguration configuration;

        public DepartmentController(IConfiguration configuration)
        {
            this.configuration = configuration;
        }

        [HttpGet]
        public IActionResult Get()
        {
            DataTable table = new DataTable();
            string query = @"SELECT * FROM dbo.Departments";

            var conString = configuration.GetConnectionString("DefaultConnection");
            using (var con = new SqlConnection(ConfigurationManager.ConnectionStrings[conString].ConnectionString))
            {
                using (var cmd = new SqlCommand(query, con))
                {
                    using (var da = new SqlDataAdapter(cmd))
                    {
                        cmd.CommandType = CommandType.Text;
                        da.Fill(table);
                    }
                }
            }
            
            return Ok(table);
        }
    }

I encounter the error on this line: using (var con = new SqlConnection(ConfigurationManager.ConnectionStrings[conString].ConnectionString))

Edit

This is the value of the conString

I even tried this code...

var conString = configuration.GetConnectionString("DefaultConnection");
            using (var con = new SqlConnection(ConfigurationManager.AppSettings[conString].ToString()))

it should be: using (var con = new SqlConnection(ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString)) — Laxmi Lal Menaria
– Laxmi Lal Menaria, Commented May 17, 2020 at 6:09
The DefaultConnection is in my appsettings.json not in the WebConfig, Sir. — Ibanez1408
– Ibanez1408, Commented May 17, 2020 at 6:12
you already have connection string so you can directly use using (var con = new SqlConnection(conString)) — Laxmi Lal Menaria
– Laxmi Lal Menaria, Commented May 17, 2020 at 6:23

mrbitzilla · Accepted Answer · 2020-05-17 06:20:46Z

1

On the SqlConnection try using the configuration object that is passed on the constructor instead of a new instance of it. Or even better the conString variable you already have (which does use the configuration instance passed on the constructor)

answered May 17, 2020 at 6:20

mrbitzilla

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2 Comments

Ibanez1408 Over a year ago

I didn't create a new instance, SIr. I just used the "coniguration" that was passed. Anyways, I tried doing what you suggested. I directly used the connection string. like so... conString2 = configuration.GetConnectionString("DefaultConnection");

mrbitzilla Over a year ago

Yes. Sorry I didn’t made myself clear. I mean, on the SqlConnection just use the conString variable instead of looking it up again.

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