Question

我有多个人连接到我的Access数据库，如果两个人碰巧同时搜索，我会收到错误。所以我这样做是为了修复它，它减少了很多错误，但我有时也会得到它。有没有更好的办法？我很确定我不应该像这样使用try catch。

public partial class Form2 : Form
{
    private OleDbConnection connection = new OleDbConnection();
    public Form2()
    {
        InitializeComponent();
        connection.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=S:\Documents\2015\Db12.accdb";
        System.Data.OleDb.OleDbConnection conn = new System.Data.OleDb.OleDbConnection();
        conn.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=S:\Documents\2015\Db12.accdb";
    }
    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);
        if (m.Msg == WM_NCHITTEST)
            m.Result = (IntPtr)(HT_CAPTION);
    }

    private const int WM_NCHITTEST = 0x84;
    private const int HT_CLIENT = 0x1;
    private const int HT_CAPTION = 0x2;

    private void lRead(string query, ListBox lbox)
    {
        OleDbCommand command = new OleDbCommand();
        command.Connection = connection;
        command.CommandText = query;
        OleDbDataReader reader = command.ExecuteReader();
        try
        {
            while (reader.Read())
            {
                lbox.Items.Add(reader["UAS"].ToString());
            }
        }
        catch (Exception ex)
        { MessageBox.Show("error LREAD" + ex); }
        finally
        {
            if (reader != null)
            { reader.Dispose(); }
        }
    }


    private void textBox1_TextChanged(object sender, EventArgs e)
    {

        try
        {
            connection.Open();
            listBox1.Items.Clear();
            lRead($"select * from Table1 where UAS Like '%{textBox1.Text}%'", listBox1);
            lRead($"select * from Table1 where Customer Like '%{textBox1.Text}%'", listBox1);
            lRead($"select * from Table1 where Description Like '%{textBox1.Text}%'", listBox1);
            lRead($"select * from Table1 where Detail Like '%{textBox1.Text}%'", listBox1);
            //select * from SomeTable Where SomeColumn Like '* PARMA *' dont use * use % 
            connection.Close();
        }
        catch
        {
            System.Threading.Thread.Sleep(500);
            try
            {
                connection.Open();
                listBox1.Items.Clear();
                lRead($"select * from Table1 where UAS Like '%{textBox1.Text}%'", listBox1);
                lRead($"select * from Table1 where Customer Like '%{textBox1.Text}%'", listBox1);
                lRead($"select * from Table1 where Description Like '%{textBox1.Text}%'", listBox1);
                lRead($"select * from Table1 where Detail Like '%{textBox1.Text}%'", listBox1);
                //select * from SomeTable Where SomeColumn Like '* PARMA *' dont use * use % 
                connection.Close();
            }
            catch
            {
                System.Threading.Thread.Sleep(500);
                try
                {
                    connection.Open();
                    listBox1.Items.Clear();
                    lRead($"select * from Table1 where UAS Like '%{textBox1.Text}%'", listBox1);
                    lRead($"select * from Table1 where Customer Like '%{textBox1.Text}%'", listBox1);
                    lRead($"select * from Table1 where Description Like '%{textBox1.Text}%'", listBox1);
                    lRead($"select * from Table1 where Detail Like '%{textBox1.Text}%'", listBox1);
                    //select * from SomeTable Where SomeColumn Like '* PARMA *' dont use * use % 
                    connection.Close();
                }
                catch
                {

                    MessageBox.Show("Error too many People Searching ");
                }

            }

        }

Answer 1

这些行没有任何用处。您分配一个新的OleDbConnection（）然后让它超出范围。连接是有限的资源，没有你将不会使用的连接。

System.Data.OleDb.OleDbConnection conn = new System.Data.OleDb.OleDbConnection();
        conn.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=S:\Documents\2015\Db12.accdb";

行

private OleDbConnection connection = new OleDbConnection();
connection.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=S:\Documents\2015\Db12.accdb";

应该将

移动到实际访问数据库的方法中。由于连接是有限的资源，因此它们实现IDisposable。任何实现IDisposable的东西都应该使用using statement来确保尽快释放相关资源。您可能会限制并发性，因为您在此处没有这样做。相反，您可以保持表单生命周期内的连接，以及垃圾收集器清理表单所需的时间。

在textBox1_TextChanged中，您会多次重复相同的代码。这很容易出错（如果您在一个地方更改代码但忘记在其他地方进行更改，该怎么办）。如果需要这种重试逻辑，请使用循环。此外，我建议您稍微随机化一下您的睡眠时间，以便多次获得错误的用户在重试之前完全睡眠的时间完全相同。将连接分配也移动到此方法中，以便在最短的时间内保持连接。

迄今为止的评论也很有用。我不会在这里重复这个建议。

如何修复此Access代码

1 个答案: