How to use SQL parameters to get dataset from SQL Server

Question

I'm working on C# project and I'm new to this technology.

I want to read some data from SQL Server 2008, and I write the following code

public User select(string username, string password)
{
    string connection = ConfigurationManager.ConnectionStrings["lawyersDBConnectionString"].ConnectionString.ToString();
    string sql = string.Format("select * from users where userName = '{0}' and password = '{1}'", username, password);

    SqlConnection con = new SqlConnection();            
    con.ConnectionString = connection;

    DataSet ds = new DataSet();
    SqlDataAdapter da = new SqlDataAdapter(sql, con);            

    User user = new User();
    DataRow dr;

    try
    {
            da.Fill(ds);
            dr = ds.Tables[0].Rows[0];

            user.Id = Convert.ToInt16(dr["userID"]);                
            user.FirstName = (string)dr["firstName"];
            user.LastName = (string)dr["lastName"];
            user.Email = (string)dr["email"];
            user.Username = (string)dr["userName"];
            user.Password = (string)dr["password"];
            user.type = (string)dr["type"];

            return user;
    }
    catch (Exception ex)
    {                
            return null;
    }
}//end of select method

But I had read an article about SQL injection, and I want to use SQL parameters to avoid this, but I don't know how.

Answer 1

This is a simple rework on your code. Not tested, but essentially it consist in adding the using statement around the disposable objects and the use of a SqlCommand with its parameters collection

string connection = ConfigurationManager.ConnectionStrings ["lawyersDBConnectionString"].ConnectionString.ToString();
string sql = "select * from users where userName = @uname and password = @pwd";

 DataSet ds = new DataSet();
 using(SqlConnection con = new SqlConnection(connection))
 using(SqlCommand cmd = new SqlCommand(sql, con))
 {
    con.Open();
    cmd.Parameters.AddWithValue("@uname", username);
    cmd.Parameters.AddWithValue("@pwd", password);

    using(SqlDataAdapter da = new SqlDataAdapter(cmd))
    {
         User user = new User();
         DataRow dr;
         da.Fill(ds);
         dr = ds.Tables[0].Rows[0];

         user.Id = Convert.ToInt16(dr["userID"]);                
         user.FirstName = (string)dr["firstName"];
         user.LastName = (string)dr["lastName"];
         user.Email = (string)dr["email"];
         user.Username = (string)dr["userName"];
         user.Password = (string)dr["password"];
         user.type = (string)dr["type"];
         return user;
    }
}

Notice how the command text doesn't contain directly the strings for user and password but a simple parameter placeholder (@uname and @pwd). These placeholders are referred as the parameters name when adding the parameters to the SqlCommand collection.

Looking at the usage of the data retrieved I strongly suggest you to look at simple ORM tools like Dapper that could directly translate all of this code in the User object