C#. Checking a SQL Data Adapter for certain values

Question

I have a database table and I am querying this table to check if a value already exists (for a login application).

I have a data adapter, but I do not know how to check if the data adapter contains the value I am looking for...

Here is the c#:

string connectionString = @"Data Source=.\SQLEXPRESS;Database=Employee;Integrated Security=true";

using (SqlConnection connection = new SqlConnection(connectionString))
  {
     SqlDataAdapter da = new SqlDataAdapter("SELECT UName FROM EVUSERS WHERE UName = '" + userName + "'", connection);
     da.Fill(dt);

     //this message displays proving the adapter contains values
     if(da != null)
       {
          MessageBox.Show("name exists");
       }
     }

I just would like to know how I can say something like

if (da contains username)  { do something }

Thank you.

Answer 1

You have to use the table's Rows.Count property.

But you should really use sql-parameters to prevent sql-injection!

SqlDataAdapter da = new SqlDataAdapter("SELECT UName FROM EVUSERS WHERE UName = @UName", connection);
da.SelectCommand.Parameters.AddWithValue("@UName", userName);
da.Fill(dt);

if(dt.Rows.Count > 0)
{
    MessageBox.Show("name exists");
}