c# - どこで / いつ connection.close() を使用するか

Question

connection.Open() と close() について誰か助けてくれませんか。いつ接続を閉じて開くかについてはよくわかりません。私にエラーを与えているコードを以下に追加します。

これについてのヒントを教えていただける方がいらっしゃいましたら、よろしくお願いいたします。接続を閉じる場所を示すコードを自由に編集して、そこから学ぶことができます。

私はまだ学生です。ありがとうございました。=)

public class LoanDAL
{
string connString = ConfigurationManager.ConnectionStrings["Oakhorizons"].ToString();
public LoanDAL()
{
    //
    // TODO: Add constructor logic here
    //
}
public DataTable getAllLoanInfoDT()
{
        using (SqlConnection conn = new SqlConnection(connString))
        {
            SqlCommand cmd2 = new SqlCommand();
            cmd2.Connection = conn;
            // cmd.CommandType = CommandType.StoredProcedure;
            cmd2.CommandText = "SELECT DISTINCT loanUpdateDate FROM LoanPortfolio WHERE (custID LIKE 'OH00002') AND (loanType LIKE 'Personal Loan')";
            cmd2.Parameters.AddWithValue("@custID", "OH00002");
            cmd2.Parameters.AddWithValue("@loanType", "Personal Loan");
            conn.Open();
            DateTime loanUpdateDate = DateTime.Now;
            SqlDataReader myReader = cmd2.ExecuteReader();
            while (myReader.Read())
            {
                loanUpdateDate = Convert.ToDateTime(myReader[0]); 
                break; 
            }

            DateTime currDateTime = DateTime.Now;

            int loanToBeAdded = (((currDateTime.Year - loanUpdateDate.Year) * 12) + currDateTime.Month - loanUpdateDate.Month) * 500;
            if (loanToBeAdded > 0)
            {
                String sql = "UPDATE LoanPortfolio SET loanPaid = loanPaid + " + loanToBeAdded.ToString() + ", LastUpdatedLoanPaidDate = " + DateTime.Now.ToString();
                sql += " WHERE (loanType LIKE 'Personal Loan') AND (custID LIKE 'OH00002')";
                cmd2.Connection = conn;
                cmd2.CommandText = sql;
                cmd2.ExecuteNonQuery();

            }
            conn.Close();
            using (SqlDataAdapter dAd = new SqlDataAdapter("SELECT * FROM LoanPortfolio where custID like 'OH00002'", conn))
            {
                DataTable dTable = new DataTable();
                dAd.Fill(dTable);
                return dTable;
            }

        }

}

//Returning a DataSet which contains all the information in the Player Table
public DataSet getAllLoanInfoDS()
{
    using (SqlConnection conn = new SqlConnection(connString))
    {

        using (SqlDataAdapter dAd = new SqlDataAdapter("SELECT * FROM LoanPortfolio where custID like 'OH00002", conn))
        {
            DataSet myDS = new DataSet();
            dAd.Fill(myDS);
            return myDS;
        }



    }
}
}