ado.net中的数据读取器

Question

I have a data reader object, which reads through say 4 rows, and I will be looping through the rows. While reading third row, I insert a row inside the same table, will my data reader be able to read the newly inserted row. If not how to achieve this functionality

Here is the code i tried.

AseCommand sessionCmd = null;
            //AseCommand selectCmd = null;
            AseCommand insertCmd = null;

            AseDataReader reader = null;

            string retCode = "Nothing returned from the Server";
            string insertStatement;
            AseConnection conn = null;
                conn = new AseConnection("Data Source='" + host + "';Port='" + port + "';UID='" + user + "';PWD='" + password + "';Database=" + db + ";");
                conn.Open();
                sessionCmd = new AseCommand("select * from dbo.DummyTable", conn);

                try
                {
                    reader = sessionCmd.ExecuteReader();
                    int count = 0;
                    while (reader.Read())
                    {

                        Console.WriteLine(reader.GetString(0));
                        count++;
                        if (count == 3)
                        {
                            //insert into table
                            insertCmd = new AseCommand("insert into DummyTable values (5)", conn);
                            insertCmd.ExecuteReader();
                        }
                    }
                }

                catch (Exception ex)
                {

                    Console.WriteLine(ex.Message);
                }

Answer 1

I found your question interesting, because I thought the context would along the lines if a row being added from another process, would the current reader see it. If I had written your test and it did not produce the result I expected, I might come to Stackoverflow and ask: is it possible to read the new row and I just did not do it right? or maybe even get an answer like: it might work sometimes but not always because of xyz ... However, you got answer three, which was 'don't bother us, we didn't sleep well last night.'

In general terms, a DataReader is a read-only forward-reading stream of tabular data sets. It is streaming the results of a query, not monitoring a table...so the query results have already been executed by the database and are being served when called,but not being updated.

Incidentally, what you did was insert a new row using an ExecuteReader command, which returned a new reader...it doesn't modify the outer reader you are looping through. You could read the results of the insert from the new reader...although its not quite clear why you would want to.

Although probably beyond the scope of your test, you might be interested in the concept of Multiple Active Result Sets which does allow you to go back and forth between two results sets on the same connection.