何时/何时使用connection.close（）

Question

任何人都可以帮我解决连接问题。打开（）和关闭（）。 我不确定何时关闭并打开连接。 下面添加了给我一个错误的代码。

如果有人能给我一个关于此的提示，我将不胜感激。 请随时编辑我的代码，显示关闭连接的位置，以便我从中学习。

我还是个学生。 谢谢。 =）

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;
        }



    }
}
}

Answer 1

您没有显式关闭连接，因为您正在使用带有sqlconnection对象的{}块。 连接将自动关闭。

第二，如果要显式关闭连接，则在完成所有数据库操作后关闭它。

例如，当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;
                }

Answer 2

这个部分：

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

关闭后，您将重新使用相同的连接。 重新打开并重复使用。 或者根本不关闭，因为你仍然using相同的块。

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，则Fill方法隐式打开DataAdapter正在使用的Connection。 如果Fill打开连接，它也将在Fill完成时关闭连接。

所以，在上面的章节“conn.close（）”无关紧要，“填充”将打开连接并关闭它。

一旦完成， using块将丢弃连接。 因此，不需要显式关闭连接。

Answer 3

Sql dataAdapter本身管理连接.it在fill命令之后打开和关闭。但是使用ExecuteReader或ExecuteNonQuery显然需要连接打开和关闭，你可以在执行nonquery和executereader命令之前打开连接，如果你的代码面临的话还有一个场景。错误和代码无法到达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，就像在一个连接中有两个命令一样，请在连接字符串中启用“MultipleActiveResultSets = True”，或者在每次连接后打开并关闭与服务器的事务（每个连接一个命令）。