How to get IdentityUser name using SqlDataReader

I have this model:

public class Model{     public IdentityUser UserId { get; set; }     public string data { get; set; }     public decimal data2 { get; set; }     public DateTime data3 { get; set; }}

And this function:

using (SqlConnection connection = new SqlConnection(connectionString)){     connection.Open();     string sql = "SELECT UserId, data, data2, data3 FROM Table;     using (SqlCommand command = new SqlCommand(sql, connection))     {         using (SqlDataReader reader = await command.ExecuteReaderAsync())         {             while (reader.Read())             {                 Model test = new Model                     {                         UserId = reader.GetString(0) // error, can not convert from Identity to string                         data = reader.GetString(1),                         data2 = reader.GetDecimal(2),                         data3 = reader.GetDateTime(3)                     };                 list.Add(test);             }         }     }}

Before this, I populated the data from the table and was able to display the data for a specific user using

command.Parameters.AddWithValue("@UserId", userId);

and I obtained the userId in the function:

protected override async Task OnInitializedAsync(){    var authState = await AuthenticationStateProvider.GetAuthenticationStateAsync();    var user = authState.User;    if (user != null)    {        userId = user.Identity.Name;    }}

I want to display on a Blazor page a table with all data from that table but I cannot get the UserId because I don't know how to read it using SqlDataReader.