ASP.Net SqlDataAdapter Error: Must declare the scalar variable

Hello Sir, 

Im getting error : 

Must declare the scalar variable "@name". 

In below code

            String query = "SELECT staff.*, holidays.date FROM abc_staff as staff INNER JOIN holidays ON staff.from_date=holidays.date where" +
                           " staff.staff_name = @name and staff.from_date = @from_date and staff.to_date = @to_date";

            SqlCommand cmd12 = new SqlCommand();
            cmd12.Parameters.AddWithValue("@name", DropDownList1.SelectedItem.Text);
            cmd12.Parameters.AddWithValue("@from_date", Convert.ToDateTime(txt_fromdate.Text));
            cmd12.Parameters.AddWithValue("@to_date", Convert.ToDateTime(txt_todate.Text));
            cmd12.CommandType = CommandType.Text;
            cmd12.CommandText = query;
            cmd12.Connection = con;
            SqlDataAdapter da = new SqlDataAdapter(query, con);
            DataTable dt = new DataTable();
            da.Fill(dt);

Please help me 

Thanks