C# 第二个问题（与原始代码有关）是，在退出Connect（）方法后，OleDbConnection对象没有句柄，因此它由GC处理，因此无论如何它都是关闭的。@Ulfric:那么，你到底试过了吗？哇-首字母缩略词发烧！数据访问对象。这些是一个将数据访问代码放入其

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第二个问题（与原始代码有关）是，在退出Connect（）方法后，OleDbConnection对象没有句柄，因此它由GC处理，因此无论如何它都是关闭的。@Ulfric:那么，你到底试过了吗？哇-首字母缩略词发烧！数据访问对象。这些是一个将数据访问代码放入其中的类，以使其与应用程序的业务逻辑分离。我第一次使用它是在Java时代。看。

private bool Connect(string username, string password)
    {
        string CONNSTRING = "Provider = MSDAORA; Data Source = ISDQA; User ID = {0}; Password = {1};";
        OleDbConnection conn = new OleDbConnection();
        string strCon = string.Format(CONNSTRING, username, password);
        conn.ConnectionString = strCon;
        bool isConnected = false;

        try
        {
            conn.Open();

            if (conn.State.ToString() == "Open")
                isConnected = true;
        }//try
        catch (Exception ex)
        {
            lblErr.Text = "Connection error";
        }//catch
        finally
        {
            conn.Close();
        }//finally

        return isConnected;
    }

private bool ValidateUserCode(string usercode)
{
    UserAccountDefine def = new UserAccountDefine();
    UserAccountService srvc = new UserAccountService();
    UserAccountObj obj = new UserAccountObj();

    bool returnVal = false;
    bool isValid = Connect(def.DB_DUMMY_USERCODE, def.DB_DUMMY_PASSWORD);
    if (isValid)
    {
        obj.SQLQuery = string.Format(def.SQL_LOGIN, usercode.ToLower(), DateTime.Now.ToString("MM/dd/yyy"));
        DataTable dt = srvc.Execute(obj, CRUD.READALL);
        if (dt.Rows.Count == 1)
        {
            returnVal = true;
        }
    }
    return returnVal;
}

        if (con != null)
        {
            con.Close();
            con.Dispose();
        }

        try
        {
            con = new OleDbConnection(connectionString);
        }
        catch (Exception ex)
        {
            MessageBox.Show("oledbConnection = " + ex.Message);
        }

        try
        {
            con.Open();
        }
        catch (Exception ex)
        {
            MessageBox.Show("connection open = " + ex.Message + "\n");
        }

private OleDbConnection Connect(string username, string password)
{
    string CONNSTRING = "Provider = MSDAORA; Data Source = ISDQA; User ID = {0}; Password = {1};";
    OleDbConnection conn = new OleDbConnection();
    string strCon = string.Format(CONNSTRING, username, password);
    conn.ConnectionString = strCon;

    try
    {
        conn.Open();

        if (conn.State.ToString() == "Open")
            return conn;
    }//try
    catch (Exception ex)
    {
        lblErr.Text = "Connection error";
    }//catch
    finally
    {
        //you don't want to close it here
        //conn.Close();
    }//finally

    return null;
}

public DataSet FetchDataSet(string sql, IDictionary paramHash) {
    var cnn = AcquireConnection();
    var rtnDS = new DataSet();
    try
    {
        var cmd = cnn.CreateCommand();
        cmd.CommandText = sql;

        SetParameters(cmd, paramHash);
        IDbDataAdapter ida = new DataAdapter { SelectCommand = cmd };
        LogSql(sql, paramHash, "FetchDataSet");
        ida.Fill(rtnDS);
    }
    catch (Exception ex)
    {
        DebugWriteLn("Failed to get a value from the db.", ex);
        throw;
    }
    finally
    {
        ReleaseConnection(cnn);
    }
    return rtnDS;
}

public MyItemType FindSomeValue(long Id)
{
    const string sql = @"SELECT something from somewhere where id=:id";
    var myParams = new Dictionary<string, long> { { "id", Id } };
    var ds = FetchDataSet(sql, myParams);

    return (from DataRow row in ds.Tables[0].Rows
            select new Item
            {
                Id = Convert.ToInt64(row["ID"], CultureInfo.InvariantCulture),
                Name = row["NAME"].ToString()
            }).FirstOrDefault();
}