Question

我有一个类可以帮助我连接到数据库启动事务并运行一些查询，一旦我完成所有查询，我提交/回滚事务。

这是我的班级

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using MySql.Data.MySqlClient;
using System.Windows.Forms;

namespace RM
{
    public class dbConnetionWT
    {
        //private OdbcConnection conn; 
        private static readonly string mServer = "localhost";
        private static readonly string mDatabase = "pos";
        private static readonly string mUid = "root";
        private static readonly string mPassword = "";
        private static readonly string mPort = "3306";
        private string conn_string = String.Format("server={0};user={1};database={2};port={3};password={4};", mServer, mUid, mDatabase, mPort, mPassword);
        private MySqlConnection conn;
        private MySqlTransaction trans;

        public dbConnetionWT()
        {
            this.conn = new MySqlConnection(this.conn_string);
            try
            {
                this.conn.Open();
            }
            catch
            {
                Common.Alert("Database Server is not reachable", "SQL Error");
            }
        }

        public void End()
        {
            try
            {
                this.conn.Close();
            }
            catch
            {
                Common.Alert("Database Server is not reachable", "SQL Error");
            }
        }


        public void BeginTransaction()
        {
            this.trans = this.conn.BeginTransaction();
        }

        public void Commit()
        {
            try
            {
                this.trans.Commit();
            }
            catch(Exception ex)
            {
                Common.Alert(ex.ToString(), "SQL Error");
            }

        }

        public void Rollback()
        {
            try
            {
                this.trans.Rollback();
            }
            catch (Exception ex)
            {
                Common.Alert(ex.ToString(), "SQL Error");
            }


        }


        // query the data base
        public IEnumerable<T> getData<T>(string query, List<MySqlParameter> pars, Func<IDataRecord, T> transform)
        {
            using (this.conn)
            using (var cmd = new MySqlCommand(query, conn))
            {
                if (pars != null)
                {
                    foreach (MySqlParameter p in pars)
                    {
                        cmd.Parameters.Add(p);
                    }
                }

                using (var rdr = cmd.ExecuteReader())
                {
                    while (rdr.Read())
                    {
                        yield return transform(rdr);
                    }
                }
            }
        }

        // query the data base
        public T getValue<T>(string query, List<MySqlParameter> pars)
        {
            T value;
            using (this.conn)
            using (var cmd = new MySqlCommand(query, conn))
            {
                if (pars != null)
                {
                    foreach (MySqlParameter p in pars)
                    {
                        cmd.Parameters.Add(p);
                    }
                }

                try
                {
                    object rawValue = cmd.ExecuteScalar();

                    if (rawValue != null)
                    {
                        value = (T)Convert.ChangeType(rawValue, typeof(T));
                    }
                    else
                    {
                        value = default(T);
                    }
                }
                catch (Exception ex)
                {
                    Common.Alert(ex.ToString(), "SQL Error");
                    value = default(T);
                    this.trans.Rollback();
                }
            }
            return value;
        }

        public bool processQuery(string strSQL, List<MySqlParameter> pars)
        {
            bool toReturn = true;

            using (this.conn)
            using (var cmd = new MySqlCommand(strSQL, conn))
            {

                if (pars != null)
                {
                    foreach (MySqlParameter param in pars)
                    {
                        cmd.Parameters.Add(param);
                    }
                }

                try
                {
                    cmd.ExecuteNonQuery();
                }
                catch (MySqlException ex)
                {
                    Common.Alert(ex.ToString(), "SQL Error");
                    toReturn = false;
                    this.trans.Rollback();
                }
            }

            return toReturn;
        }
    }
}

以下是我遇到问题时的使用方法

 bool hasSqlError = false;
 string sql2 = " INSERT INTO products "
 + " (productUPC, productName, price, createdBy, departmentID, vendorID, productDescription) "
 + " VALUES('123', 'Name', '29.99', '1', '2', '3', 'This is a test')";

if (!dbwt.processQuery(sql2, null))
{
    hasSqlError = true;
}

if (!hasSqlError)
{
    dbwt.Commit();
    dbwt.End();
    this.Close();
}
else
{

    dbwt.Rollback();
}

但在尝试提交dbwt.Commit();

时，我一直收到错误消息

这是我得到的异常错误 enter image description here

如何更正此问题？即使我在构造函数中打开连接，我也不明白为什么会出现此错误？

Answer 1

请注意以下代码：

    public T getValue<T>(string query, List<MySqlParameter> pars)
    {
        T value;
        using (this.conn)

如果您在某个时刻致电getValue<T>，请执行

后的阻止

        using (this.conn)

超出范围，将调用this.conn.Dispose()，关闭连接。

Answer 2

using (this.conn)方法中有processQuery()，using语句会导致您的连接关闭。所以错误信息是有道理的。

您已经在End()方法中明确关闭了连接，因此请省略以下行：

using (this.conn)

同样FWIW，您可能希望确保在回滚后关闭连接：

if (!hasSqlError)
{
    dbwt.Commit();
}
else
{
    dbwt.Rollback();
}
dbwt.End();
this.Close();

或者，即使在抛出异常的情况下也要确保连接已关闭：

try
{
    if (!hasSqlError)
    {
        dbwt.Commit();
    }
    else
    {
        dbwt.Rollback();
    }
    this.Close();
}
finally
{
    dbwt.End();
}

C＃MySQL提交事务不起作用（连接必须有效并且打开以提交事务）

2 个答案: