Re: Returning Null value instead of contents of field
From: Stephen Howe (stephenPOINThoweATtns-globalPOINTcom)
Date: 02/24/05
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Date: Thu, 24 Feb 2005 16:50:14 -0000
> If I am correct in my understanding of the situation.
>
> When I use a Forward only cursor in SQL Server I can only read the
contents
> of the a nText field once.
>
> Does this mean that I should copy the contents of the nText field into a
> local variable before I use it or change my cursor?
Very likely. I have never tested this (but I will do so sometime). The
ForwardOnly cursor is very, very very limited in what functionality it
provides you. It is the price you pay for its speed. I like it. I use
ForwardOnly cursors to build small lookup-tables in memory using binary
search.
> Is there a best practice article I can read to explain how I should be
doing
> this?
No <groan> unfortunately. I wish there was.
I draw my knowledge from a variety of sources:
1. Bill Vaugns books and articles. It is the closest you will get to "Best
Practice".
I liked the original brown-covered "ADO Examples and Best Practices" which I
have.
I also have the purple-covered successor which covers ADO.NET in the 2nd
half.
See
http://www.betav.com/Files/Books/books.htm
See Articles
http://www.betav.com/articles.htm
See also
http://www.windowsitpro.com/SQLServer/Article/ArticleID/16272/16272.html
ADO Performance "Best Practices"
http://www.betav.com/Files/Content/Whitepapers/ADO%20Performance.htm
2. Microsofts MSDN site on ADO. I have noticed that Microsoft over the years
have, very quietly updated the documentation. So it pays to go and relook on
various ADO methods, properties, events just to see if Microsoft have added
any extra info on it that might make a difference to your code.
See
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ado270/htm/dasdkadooverview.asp
and click on the links at the bottom
3. There is the MDAC document on improving ADO performance by Suresh Kannan.
Very good. A little dated by now (nothing about ADO's Record object for
singleton SELECTs) but still very relevant. See
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnmdac/html
/improvperf.asp
I also pay attention to dynamic properties that only exist once object is
opened etc.
You can also read up on various providers in OLE DB documentation but it is
hard work and can be unrewarding. It is very esoteric and you maybe asking
yourself, "when would I ever use such a property or change the default?".
4. Carl Prothmans ADO & ADOX FAQ site is worth reading.
See
http://www.able-consulting.com/ADO_Faq.htm
http://www.able-consulting.com/ADOX_Faq.htm
5. If you use VC++, the temporary headers and inlines generated by #import
are worth looking at . I have sometimes compared different versions produced
by using different MDACs to try and work out what Microsoft have "improved
in ADO" that is not mentioned.
Stephen Howe
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