Question

i 正在使用VS。 2008年网络,2005年有MSQ服务器,开发一个窗户申请表,但每小时一度出现新的链接或校外错误。

在我目前的法典中,这一联系在进行问答之后开启了但又充满活力的工作。也许在建立新的行文或新的数据来源时会遇到问题,而不能满足连接“努力”

这是我的法典。

/////////
private void button1_Click(object sender, EventArgs e)
    {
        try
        {
            //setData();
            string ConnectingString = @"Data Source=SERVER1SQLEXPRESS;Initial Catalog=Alkawthar;Integrated Security=True;Pooling=False";
            qry = "SELECT * FROM Table1";
            //reader = db.select_data(qry);
            ds1 = new DataSet();
            conn = new SqlConnection(ConnectingString);

            conn.Open(); 
            MessageBox.Show("connection opened");
            da.Fill(ds1,"Workers");
            NavigateRecords();
            MaxRows = ds1.Tables["Workers"].Rows.Count;
            string sql = "SELECT * From tblWorkers";
            da = new System.Data.SqlClient.SqlDataAdapter(sql, conn);
            conn.Close();
            MessageBox.Show("connection closed");
            conn.Dispose();
        }
        catch (Exception ex)
        {
            MessageBox.Show("exception");
            MessageBox.Show(ex.Message);
        }
    }
/////////////////

Fill throws an exception also when i use reader it return null although there is data in DB thanks

Answer 1

几点意见;

Like Turrau and Rune say, your stuff is in the wrong order. Open connection, Execute SQL - Get raw data, close connection. Then do your counting, etc.
Don t put message box or logging calls anywhere in between the connection opening and closing. This has burned me before, where the those calls can affect the SQL call because they fudge the exception details and make it difficult to trace. This is also applicable when using a SQL data reader.
Put the SQL stuff in a using block.

......

    string _connStr = @"Data Source=SERVER1SQLEXPRESS;Initial Catalog=Alkawthar;Integrated Security=True;Pooling=False";
    string _query = "SELECT * FROM Workers";
    DataSet _ds = new DataSet();

    try
    {

        using (SqlConnection _conn = new SqlConnection(_connStr))
        {
            SqlDataAdapter _da = new SqlDataAdapter(_query, _conn);
            _conn.Open();
            _da.Fill(_ds);
        }

        // insert null dataset or invalid return logic (too many tables, too few columns/rows, etc here.


        if (_ds.Tables.Count == 1)
        { //There is a table, assign the name to it.
            _ds.Tables[0].TableName = "tblWorkers";
        }

        //Then work with your tblWorkers

    }
    catch (Exception ex)
    {
        Console.Write("An error occurred: {0}", ex.Message);
    }

Answer 2

The most obvious problem here is that you access the SqlDataAdapter before initializing it. That will cause a null reference exception. Try to move the line da = new SqlDataAdapter(...) to the line before you do the da.Fill(...).

Edit:

无,等待! 我看到你在那里做两次问答和两次填满。你们需要在完成第一次补选之前先启动SqlDataAdapter。然后,你就应当排除无参照例外。

Edit再次重申:

此外,正如所评论的那样,你不需要同时使用<条码>SqlConnection。近和<代码>SqlConnection。处置方法。只要你使用SqlDataAdapter,你甚至不需要填写。关于连接的开放,对于“Fill”方法,你们都会这样做。只要连接开始关闭,则在接通时将再次关闭。

Answer 3

让我看到,你在开始使用数据Adapter。您是否收到?

da.Fill(ds1,"Workers"); 
// ...
da = new System.Data.SqlClient.SqlDataAdapter(sql, conn);

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