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谁能帮助我关于connection.Open（）和close（）。我不太确定何时关闭和打开连接。下面添加了给我错误的代码。

如果有人可以给我一个提示，我将不胜感激。请随时编辑我的代码以显示关闭连接的位置，以便我从中学习。

我还是个学生。谢谢你。=)

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;
        }



    }
}
}
4

3 回答 3

2

您没有显式关闭连接，因为您将 {} 块与 sqlconnection 对象一起使用。连接将自动关闭。

其次，如果您想明确关闭连接，则在所有数据库操作完成后关闭它。

例如，当您的适配器填充操作完成时关闭它。

....
....
....
using (SqlDataAdapter dAd = new SqlDataAdapter("SELECT * FROM LoanPortfolio where custID like 'OH00002'", conn))
                {
                    DataTable dTable = new DataTable();
                    dAd.Fill(dTable);
                    conn.Close();
                    return dTable;
                }
于 2013-07-30T09:35:35.523 回答
0

Sql dataAdapter 本身管理连接。它在填充命令后打开和关闭，但是使用 ExecuteReader 或 ExecuteNonQuery 明确需要打开和关闭连接，您可以在执行 nonquery 和 executereader 命令之前打开连接，如果您的代码面临另一种情况错误和代码未到达conn.close(); 命令 。

   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");

            DateTime loanUpdateDate = DateTime.Now;
            try
            {
             conn.Open();
            SqlDataReader myReader = cmd2.ExecuteReader();
            while (myReader.Read())
            {
                loanUpdateDate = Convert.ToDateTime(myReader[0]); 
                break; 
            }
               conn.Close();   
            DateTime currDateTime = DateTime.Now;
            }
            Catch(Exception Ex)
            {//Close connection in case of any exception .
              conn.Close();
            }
            int loanToBeAdded = (((currDateTime.Year - loanUpdateDate.Year) * 12) + currDateTime.Month - loanUpdateDate.Month) * 500;
            if (loanToBeAdded > 0)
            {
               try
               {
                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;
                 conn.Open();
                cmd2.ExecuteNonQuery();
                conn.Close();
                }
                Catch(Exception Ex)
                 {
                 //Close connection in case of exception .
                  Conn.close()
                  throw Ex;
                 }
            }            
            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;
        }



    }
}
}

您的连接字符串需要添加“MultipleActiveResultSets=True”。如果您使用多个命令，例如在单个连接中有两个命令，请在连接字符串中启用“MultipleActiveResultSets=True”，或者每次打开并关闭与服务器的事务（每个连接一个命令）。

于 2013-07-30T09:59:26.623 回答
0

本节：

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

您在关闭它后重新使用相同的连接。重新打开并重新使用。或者根本不要关闭，因为您仍然在同一个using街区。

更新：MSDN： http: //msdn.microsoft.com/en-us/library/bh8kx08z (v=vs.100).aspx

如果发现连接尚未打开，Fill 方法会隐式打开 DataAdapter 正在使用的连接。如果 Fill 打开了连接，Fill 完成后它也会关闭连接。

因此，在上面的“conn.close()”部分中，“填充”将打开连接并关闭它。

一旦完成，该using块将断开连接。因此，不需要显式关闭连接。

于 2013-07-30T09:36:07.273 回答