请问我的代码中存在什么问题 [英] pls suggest me what is the problem in my code

问题描述

亲爱的朋友。

i有数据表，我用数据库表的值填充这个数据表，其中已经有一行但是当我使用连接模式加载数据表时它不给我1行数据对我来说，为什么





建议我

我的代码是这个







string sql =select * from+ checkedListBox2.SelectedItem.ToString（）+;

Npgsql.NpgsqlCommand cmd = new Npgsql.NpgsqlCommand（sql，con）;

dear frnds.
i have datatable and i am fill this datatable with the value of database table which have already a row in it but when i m load datatable using connected mode it give not me 1 row data to me, why


suggest me
my code is this



string sql = "select * from " + checkedListBox2.SelectedItem.ToString() + "";
Npgsql.NpgsqlCommand cmd = new Npgsql.NpgsqlCommand(sql, con);

using (Npgsql.NpgsqlDataReader rdr = cmd.ExecuteReader())
                            {
                                while (rdr.Read())
                                {
                                   
                                    dbdt.Load(rdr)
}
 for (int b = 0; b < dbdt.Rows.Count; )
                                    {
 string str = dbdt.Rows[b][chklistindex2].ToString();

                                        if (strg == str)
                                        {
                                            MessageBox.Show("find");
                                        }
                                        else if (strg!=str)
                                            {
                                                b++;
 
                                            }                                        
                                        else
                                        {
                                            using (var conn = new Npgsql.NpgsqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["test"].ToString()))
                                            using (var cmd1 = conn.CreateCommand())
                                            {
                                                conn.Open();
                                                cmd1.CommandText = "insert into " + checkedListBox2.SelectedItem.ToString() + " ( " + checkedListBox2.SelectedItem.ToString() + " ) values('" + strg + "')";
                                                var result = cmd1.ExecuteNonQuery();
                                            }
                                        }
                                    }
                         


this is my code and my database table (f_name)


it have 2 column id and f_name
and value in it is 1 and kavita respectively on first index

but my above code dose not load this data into datatable


why if i am add a new row in database then it load the data form second row in datatable


pls help me

推荐答案

简单：你读了（并因此丢弃）第一个在你打电话时记录在阅读器中阅读：

Simple: You read (and thus discard) the first record in the reader when you call Read:

while (rdr.Read())
{
    dbdt.Load(rdr);

Read读取一行，并将其从读取器中删除：所以当你调用Load时，行不再可用。

尝试

Read reads a row, and removes it from the reader: so when you call Load the row is no longer available.
Try

if (rdr.HasRows)
   {
   dbtb.Load(rdr);

但请不要这样做！不要连接字符串以构建SQL命令。它让您对意外或故意的SQL注入攻击持开放态度，这可能会破坏您的整个数据库。请改用参数化查询。

But please, don't do things like that! Do not concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Use Parametrized queries instead.

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