How to remove the sql injection from this query and make it working well?

Question

I am a new ASP.NET developer and I am developing a web-based application in which there is a menu bar that has many options. Some of these options will be displayed only to the Admin. There is a logic behind the system to check whether the user is an admin or not. If yes, the options will be displayed. I wrote the method but I have a sql injectiom and I want to remove it.

For your information, I have the following database design:

• Users table: NetID, Name, Title
• Admins table: ID, NetID

Here's the C# method:

private bool isAdmin(string username)
{
        string connString = "Data Source=appSever\\sqlexpress;Initial Catalog=TestDB;Integrated Security=True";
        string cmdText = "SELECT ID, NetID FROM dbo.Admins WHERE NetID = '" + NetID + "')";
        using (SqlConnection conn = new SqlConnection(connString))
        {
            conn.Open();
            // Open DB connection.
            using (SqlCommand cmd = new SqlCommand(cmdText, conn))
            {
                SqlDataReader reader = cmd.ExecuteReader();
                if (reader != null)
                    if (reader.Read())
                        if (reader["ID"].Equals(1))
                            return true;
                return false;
            }
        }
    }

I tried to change it by doing the changing the third line to:

string cmdText = "SELECT ID, NetID FROM dbo.Admins WHERE NetID = @NetID)";

But I got the following error and I don't know why:

Must declare the scalar variable "@NetID".

Could you please help me in solving this?

**UPDATE:

After updating the code to the following:
    private bool isAdmin(string username)
    {
        string NetID = username;
        string connString = "Data Source=appServer\\sqlexpress;Initial Catalog=TestDB;Integrated Security=True";
        string cmdText = "SELECT ID, NetID FROM dbo.Admins WHERE NetID = @NetID";
        using (SqlConnection conn = new SqlConnection(connString))
        {
            conn.Open();
            // Open DB connection.
            using (SqlCommand cmd = new SqlCommand(cmdText, conn))
            {
                cmd.Parameters.AddWithValue("@NetID", NetID);
                SqlDataReader reader = cmd.ExecuteReader();
                if (reader != null)
                    if (reader.Read())
                        if (reader["NetID"] == username)
                            return true;
                return false;
            }
        }
    }

I got the following error:

Incorrect syntax near ')'.

How to fix this problem?

Answer 1

You need to pass a value for your @NetID parameter:

cmd.Parameters.AddWithValue("@NetID", NetID);

Answer 2

Try this

 private bool isAdmin(string username)
 {
    string connString = "Data Source=appSever\\sqlexpress;Initial Catalog=TestDB;Integrated Security=True";
    string cmdText = "SELECT ID, NetID FROM dbo.Admins WHERE NetID = @NetID)";
    using (SqlConnection conn = new SqlConnection(connString))
    {
        conn.Open();
        // Open DB connection.
        using (SqlCommand cmd = new SqlCommand(cmdText, conn))
        {
            cmd.Parameters.AddWithValue("@NetID", NetID);
            SqlDataReader reader = cmd.ExecuteReader();
            if (reader != null)
                if (reader.Read())
                    if (reader["ID"].Equals(1))
                        return true;
            return false;
        }
    }
 }