read & update using reader

[PIEBALDconsult]

Mycroft Holmes wrote:

(relearning) Oracle.

But not in C with Pro*C I bet.

[MDNadeemAkhter]

:-D

[Brady Kelly]

It is maybe neater to not use a reader, but rather a DataTable and a TableAdapter. Then you can loop through the table rows, update the is_sent on each row as you process it, and then call Update. Something like this:

using (var ad = new SqlDataAdapter("sp\_send\_pending\_sms", ConfigurationManager.ConnectionStrings\["SQLdb"\].ConnectionString))
{
    ad.SelectCommand.CommandType = CommandType.StoredProcedure;
    var dt = new DataTable();
    ad.Fill(dt);

    // blah blah blah. do your work.
    ad.AcceptChangesDuringUpdate = true;
    ad.Update(dt);
}

If the list is long, you may want to call Update every n rows, not just at the end.

[Gary Huck]

Yes, something like that is what you need. The ExecuteReader() method, as the name implies, is only for selecting (reading) data. p.s. Stored procedures are a great way to go!

[Gary Huck]

Tell us why one should NOT use stored procedures, as you state.

[Fabio Franco]

PIEBALDconsult wrote:

I have never understood the reason so many devs use the DataAdapter and load a whole butt-load of data at once when they don't use it all at once.

When you know there will never be too much data and that it will not have impact on system resources and when you want to work with data in a disconected state. There are good uses for both approaches, that's why they exist. Beeing wise to use them where they fit is another story, can't speak for anyone.

[Spectre_001]

You can not update through a DataReader. It retreives a read-only, forward-only stream of data one record at a time. If I read your question correctly, you are doing some processing on each record after reading, then need to set a flag in the database to indicate that record has been processed. You will need a second connection and comand object for this. You can't use the same connection/command as the DataReader because it keeps it's connection open internally throughout it's lifetime. The best way to accomplish this will vary slightly depending on how many records you expect to process and whether the processing will run a long time (cumulative). For a relatively short run: 1. Open SQLConnection for updating and attach to SQLCommand 2. Read next record from DataReader 3. Perform needed processing 4. Generate update SQL for current record 5. Use SQLCommand to run update SQL 6. Repeat steps 2 - 5 until last record has been processed and updated 7. Close and destroy update SQLConnection/SQLCommand For a long run: 1. Create SQLConnection for updating and attach to SQLCommand 2. Read next record from DataReader 3. Perform needed processing 4. Generate update SQL for current record 5. Open SQLConnection for update 6. Use SQLCommand to run update SQL 7. Close SQLConnection 8. Repeat 2 - 7 until last record has been processed and updated 9. Close and destroy update SQLConnection/SQLCommand Hope this answers your question and helps out.

Kevin Rucker, Application Programmer QSS Group, Inc. United States Coast Guard OSC Kevin.D.Rucker@uscg.mil "Programming is an art form that fights back." -- Chad Hower

[Miroslav Bucko]

That article is from 2003. And yeah, i'm wondering too, why?

[Jason Christian]

Short answer - You can't. It is a data READER - not an updater. It's not like opening a recordset in VB6. You need to ExecuteSQL with appropriate SQL to udpate the records (i.e. UPDATE table SET field=value WHERE key=id). To do it the way you want it would better to use a DataSet or something a little more robust - plenty of info on MSDN.

[Mycroft Holmes]

Nothing fundamental has changed in databases since 2003 so the premise of the article is still very valid, I just don't agree with it.

Never underestimate the power of human stupidity RAH

[PIEBALDconsult]

GamleKoder wrote:

is only for selecting (reading) data.

No it isn't; it can execute any SQL statement (even a list of them if the particular database engine supports it) and it underlies all the other ADO.net data manipulation methody, so you're using it whether you know it or not.

[PIEBALDconsult]

Spectre_001 wrote:

You can not update through a DataReader

No, but you can through ExecuteReader. In your scenarios... generate a parameterized update command up front and then set the parameters for each row and execute -- no need to keep generating the same SQL statement.

[Spectre_001]

That dosen't help if he needs to read, process, then update. :-D

Kevin Rucker, Application Programmer QSS Group, Inc. United States Coast Guard OSC Kevin.D.Rucker@uscg.mil "Programming is an art form that fights back." -- Chad Hower

[James Lonero]

Using stored procedures, more of a good thing than using dynamic SQL? The article makes a good argument about changes legacy systems. The need to change the stored procedures will break code, or adding more stored procedures adds extra (duplicate) overhead. If just adding a new column to a table requires adding a new input parameter, we will need to add a new stored procedure to handle it. Of course, the old stored procedure can call the new stored procedure with a dummy argument for the new input value. On the other hand, using dynamic SQL may require revision to add the new parameter (where it is needed). The down side is that legacy code that uses the database will need to have its SQL updated. Not only will the new application making use of the "improved" database have the changes, but all of the older applications will need to change, if the new database is used with them. And, there is the possibility of SQL injection attacks, depending on how you store your SQL in your application. Updating Stored Procedures is akin to the old days of COM programming. There was a rule, at one time, that said we should not change a published interface, but make a new interface. This also was applied to the methods as well. And, a good programmer will do the least amount of work to get the job done efficiently. You must decide which method is best for you.