如何关闭sqldatareader

int id;
        string tring = "Data Source=(local);Initial Catalog=studywebsite;Integrated Security=True;";
        SqlConnection con = new SqlConnection(tring);
        con.Open();
        string sql = "select book_id from book";
        
        SqlDataReader reader;
        
        using (SqlCommand com = new SqlCommand(sql, con))
        {
            reader = com.ExecuteReader();            while (reader.Read())
            {
                com.CommandType = CommandType.Text;                reader = com.ExecuteReader();                id = reader.GetInt16(0);
                SqlDataSource2.InsertParameters["title_list"].DefaultValue = titlelist.Text;
                SqlDataSource2.InsertParameters["book_sort"].DefaultValue = booksort1.SelectedItem.ToString();
                SqlDataSource2.InsertParameters["title_matter"].DefaultValue = titlematter.Text;
                SqlDataSource2.InsertParameters["book_id"].DefaultValue = id.ToString();
                SqlDataSource2.Insert();
                titlelist.Text = "";
                booksort1.Text = "";
                titlematter.Text = "";
            }
            
            con.Close();我忘了关闭reader了，请问一下我怎样才能关闭上次打开的reader呢？