在C＃中使用OleDbDataReader时无法从Access数据库读取字段信息

Question

i wrote a form based C# program to read/write to a access data base. in it i have 2 tables: User and Item the following code should have read a spesific field from the User table and return it to me based on the field number but, i can't get it to work for some reason... help would be good at this point (4AM)

 public string UserGetField(int user_id,int field)
        {
            string found="";
            string command="";
            switch (field)
            {
                case 1://first_name
                    command+= "first_name";
                    break;
                case 2://last_name
                      command+= "last_name";
                    break;
                case 3://grade
                      command+= "grade";
                    break;
                case 4://phone
                      command+= "phone";
                    break;
                case 5://address
                      command+= "address";
                    break;
                case 6://item
                    command += "item";
                    break;
            }
            cmd.CommandText = "select '" + command + "' from User where user_id = '" + user_id + "'";
            con.Open(); // open the connection
            OleDbDataReader dr = cmd.ExecuteReader();
            while (dr.Read())
            {
                found += dr["first_name"].ToString();
            }
            con.Close();
            return found;
        }

Answer 1

try this:

    cmd.CommandText = "select [" + command + "] from User where user_id = '" + user_id + "'";

Also, you're dynamically choosing the select field but always looking for the first_name field in the result. Change to

        while (dr.Read())
        {
            found += dr[0].ToString();  // first field value
        }

Answer 2

Try this ?

    public string UserGetField(int user_id, int field)
    {
        var columns = new string[] { "first_name", "last_name", "grade", "phone", "address", "item" };

        var list = new List<string>();
        string command = columns[field - 1];
        var sql = string.Format("select '{0}' from User where user_id = '{1}'", command, user_id);
        var conStr = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + Directory.GetCurrentDirectory() + @"\test.mdb"; //

        using (var conn = new OleDbConnection(conStr))
        {
            conn.Open();
            var cmd = new OleDbCommand(sql, conn);
            OleDbDataReader dr = cmd.ExecuteReader();
            while (dr.Read())
            {
                list.Add(dr[command].ToString());
            }
        }
        return string.Join(",", list.ToArray());
    }

Answer 3

this is the final version that works... swithced from table named User to Kids and made someother changes

 public string UserGetField(int user_id,int field)
        {
            string found="";
            string command="";
            switch (field)
            {
                case 1://first_name
                    command+= "first_name";
                    break;
                case 2://last_name
                      command+= "last_name";
                    break;
                case 3://grade
                      command+= "grade";
                    break;
                case 4://phone
                      command+= "phone";
                    break;
                case 5://address
                      command+= "address";
                    break;
                case 6://item
                    command += "item";
                    break;
            }
            cmd.CommandText = "SELECT " + command + " FROM Kids WHERE user_id = " + user_id + "";
            con.Open(); // open the connection
            OleDbDataReader dr = cmd.ExecuteReader();
            while (dr.Read())
            {
                found = dr[command].ToString();      
            }
            con.Close();
            return found;
        }