ExecuteNonQuery requires an open and available Connection. The connection's current state is closed.

今天调试一个监控程序，放到环境里发现不写库，于是给SQL执行类异常事件做了个日志，发现报：

ExecuteNonQuery requires an open and available Connection. The connection's current state is closed.

左看右看，没问题呀，后来才想起，using里没有执行db.Open，打开数据库连接。

    public class SQLHelper : IDisposable
    {
        private IntPtr handle;
        private readonly Component component = new Component();
        private bool disposed;
        private readonly string _connstr = Config.ConnectionString;

        #region 执行SQL语句，返回影响行数
        /// <summary>
        /// 执行查询，返回影响行数
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public int iExecute(string sql)
        {
            int intTemp;
            try
            {
                using (var db = new SqlConnection(_connstr))
                {
                    db.Open();
                    var cmd = new SqlCommand(sql, db) {CommandType = CommandType.Text};
                    intTemp = cmd.ExecuteNonQuery();
                    db.Close();
                }
            }
            catch(Exception ex)
            {
                FileHelper.AppendFile("D:\\Log.txt", string.Format("{0}[{1}][{2}]",sql ,ex.Message,_connstr));
                intTemp = 0;
            }
            return intTemp;

        }
        #endregion

        #region 执行SQL语句，返回表结果
        /// <summary>
        /// 查询返回DataSet
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public DataSet pExecute(string sql)
        {
            var ds = new DataSet();
            try
            {
                using (var db = new SqlConnection(_connstr))
                {
                    db.Open();
                    var dr = new SqlDataAdapter();
                    var cmd = new SqlCommand(sql, db) {CommandType = CommandType.Text};
                    dr.SelectCommand = cmd;
                    dr.Fill(ds);
                    ds = (ds.Tables.Count == 0) ? null : ds;
                    db.Close();
                }
            }
            catch{}
            return ds;
        }
        #endregion

        #region 执行存储过程，返回查询的表结果
        /// <summary>
        /// 执行存储过程，返回查询的表结果
        /// </summary>
        /// <param name="produceName"></param>
        /// <param name="param"></param>
        /// <returns></returns>
        public DataSet pExecute(string produceName, SqlParameter[] param)
        {
            var ds = new DataSet();
            try
            {
                using (var db = new SqlConnection(_connstr))
                {
                    db.Open();
                    var cmd = new SqlCommand {Connection = db,CommandType = CommandType.StoredProcedure,CommandText = produceName};
                    var dr = new SqlDataAdapter();
                    foreach (var t in param)
                    {
                        cmd.Parameters.Add(t);
                    }
                    dr.SelectCommand = cmd;
                    dr.Fill(ds);
                    db.Close();
                }
            }
            catch (Exception){}
            return ds;
            
        }
        #endregion

        #region 执行存储过程，返回影响行数
        /// <summary>
        /// 执行存储过程，返回影响行数
        /// </summary>
        /// <param name="produceName"></param>
        /// <param name="param"></param>
        /// <returns></returns>
        public int iExecute(string produceName, SqlParameter[] param)
        {
            int intTemp = 0;
            try
            {
                using (var db = new SqlConnection(_connstr))
                {
                    db.Open();
                    var cmd = new SqlCommand
                                  {
                                      Connection = db,
                                      CommandType = CommandType.StoredProcedure,
                                      CommandText = produceName
                                  };
                    foreach (var t in param)
                    {
                        cmd.Parameters.Add(t);
                    }
                    intTemp = cmd.ExecuteNonQuery();
                    db.Close();
                }
            }
            catch (Exception){}
            return intTemp;
        }
        #endregion

        #region Dispose实现
        public void Dispose()
        {
            try
            {
                Dispose(true);
                GC.SuppressFinalize(this);
            }
            catch (Exception)
            {
            }

        }
        private void Dispose(bool disposing)
        {
            if (!disposed)
            {
                if (disposing)
                {
                    component.Dispose();
                }
                CloseHandle(handle);
                handle = IntPtr.Zero;
                disposed = true;
            }
        }
        [System.Runtime.InteropServices.DllImport("Kernel32")]
        private extern static Boolean CloseHandle(IntPtr handle);
        #endregion


    }