If you do any development using SharePoint's web services you've undoubtedly run across the evil CAML beast rearing it's ugly head to devour your nicely structured markup. For instance, if you invoke GetListItems() to retrieve the column values of each item in a list, you have the option of passing in a CAML query to return specific records or a blank value to get the whole enchilada. The SDK is quite helpful, as it documents how this specific query should look. If, for example, you want a particular record with the title "Yellow", provide the following CAML:
<Query><Where><Eq><FieldRef name="Title"><Value Type="Text">Yellow</Value></Eq></Where></Query>
Simple, no? Well, not quite so simple. Try as you might, this query will never return just those items whose Title column is equal to "Yellow". Instead, the web service will happily ignore your fancy little CAML fragment and give you all the records in the list. Alas, no amount of cursing, head beating, keyboard throwing or foot stomping will make it otherwise. I assure you, I have tried all of those methods, and many more, to no avail. What DOES work is simply removing the <Query> and </Query> tags, like so:
<Where><Eq><FieldRef name="Title"><Value Type="Text">Yellow</Value></Eq></Where>
What's that you say? That's not how the SDK says it should be done? You spent hours searching the newsgroups and nobody once mentioned this little bit of CAML trickery? I feel your pain, my friend, believe me, I do. Were it not for my innate stubbornness and determination to beat SharePoint at it's own game, I would have given up on this vexing problem many moons ago. What can I tell you - CAML is a mysterious creature and we know not it's wild and wily ways. Now go ye forth and slay that noxious Query fiend - or at least stab at it until the next time it bites you on the rear!