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How to make database changes visible to your application?I am using VS2005 (C#) and SQL Server 2000. How can I make sure that: 1. Client A queries info from database and displays it in a list view or other controls on a form. If Client B changes some of this info that is displayed by client A, clint A gets its info updated 2. If clint B tries to delete data currently displayed by client A, the attempt should fail. How can I make sure that database data displayed on the client's forms is always newest data? Any help will be appreciated. _dino_ This has been discussed a thousand times on this list and elsewhere. I
suggest researching "concurrency", "locking", "pessimistic" and other related terms in the list archives. If you still can't find an answer or don't understand what you find, come back and we'll offer a few suggestions. -- Show quote____________________________________ William (Bill) Vaughn Author, Mentor, Consultant Microsoft MVP INETA Speaker www.betav.com/blog/billva www.betav.com Please reply only to the newsgroup so that others can benefit. This posting is provided "AS IS" with no warranties, and confers no rights. __________________________________ "Dino Buljubasic" <d***@noplacelikehome.com> wrote in message news:2214v1lhlieqd60807l1vp0dp0i8fdln1q@4ax.com... > Hi, > > I am using VS2005 (C#) and SQL Server 2000. > > How can I make sure that: > > 1. Client A queries info from database and displays it in a list view > or other controls on a form. If Client B changes some of this info > that is displayed by client A, clint A gets its info updated > > 2. If clint B tries to delete data currently displayed by client A, > the attempt should fail. > > How can I make sure that database data displayed on the client's forms > is always newest data? > > Any help will be appreciated. > > _dino_ Dino,
What you are trying to do is very nearly impossible using VS.Net and ADO.Net. Most .Net applications handle concurrency issues when a client actually attempts to update the database. Why won't that approach work for you? Kerry Moorman Show quote "Dino Buljubasic" wrote: > Hi, > > I am using VS2005 (C#) and SQL Server 2000. > > How can I make sure that: > > 1. Client A queries info from database and displays it in a list view > or other controls on a form. If Client B changes some of this info > that is displayed by client A, clint A gets its info updated > > 2. If clint B tries to delete data currently displayed by client A, > the attempt should fail. > > How can I make sure that database data displayed on the client's forms > is always newest data? > > Any help will be appreciated. > > _dino_ > Ah, I would not go that far. Yes, this is possible with ADO.NET but it does
not help much. Even with ADO classic, a server-side cursor still has to be polled to return the current state of the database rows you're monitoring. Typically, the server does not have a "back channel" to the clients so it does not have a way to notify them that changes have been made. SqlNotification can do this, but it can be very expensive in lost server performance unless used wisely. As far as locking is concerned, that is also possible. You can create a scoped transaction that simulates a pessimistic cursor on the server that prevents others from changing selected rows--but again, this is problematic (to say the least) if not handled wisely. Most developers faced with this situation poll the server for changes in focused data regions, use focused server-side cursors (which are still possible using ANSI CREATE CURSOR commands) or resort to systems where there aren't collisions in the first place. The key here is to focus the queries on easily retrieved rowsets--not entire tables or the product of a complex JOIN. hth -- Show quote____________________________________ William (Bill) Vaughn Author, Mentor, Consultant Microsoft MVP INETA Speaker www.betav.com/blog/billva www.betav.com Please reply only to the newsgroup so that others can benefit. This posting is provided "AS IS" with no warranties, and confers no rights. __________________________________ "Kerry Moorman" <KerryMoor***@discussions.microsoft.com> wrote in message news:76AC957F-5F42-4D59-9701-B047DFF8742D@microsoft.com... > Dino, > > What you are trying to do is very nearly impossible using VS.Net and > ADO.Net. > > Most .Net applications handle concurrency issues when a client actually > attempts to update the database. Why won't that approach work for you? > > Kerry Moorman > > > "Dino Buljubasic" wrote: > >> Hi, >> >> I am using VS2005 (C#) and SQL Server 2000. >> >> How can I make sure that: >> >> 1. Client A queries info from database and displays it in a list view >> or other controls on a form. If Client B changes some of this info >> that is displayed by client A, clint A gets its info updated >> >> 2. If clint B tries to delete data currently displayed by client A, >> the attempt should fail. >> >> How can I make sure that database data displayed on the client's forms >> is always newest data? >> >> Any help will be appreciated. >> >> _dino_ >> Bill,
Yes, that is why I said it is "very nearly impossible" "using ADO.Net". With a connected technology like ADO it can be done brute force with pessimistic locking (un-scalable and close to un-workable if you have a bunch of users). With ADO.Net it can be simulated with transactions (often talked about but I suspect rarely implemented). But these are kludges that I wouldn't recommend to anyone that did not have a good bit of experience already. That experienced person probably would not need to ask how to do it (specific questions maybe but not general ones). So in that context I will stick by my response that it is very nearly impossible using ADO.Net. Of course, the suggestions you made, especially focusing on retrieving small amounts of data and not entire tables, etc., will help mitigate the problem and are good ideas in general. Kerry Moorman Show quote "William (Bill) Vaughn" wrote: > Ah, I would not go that far. > [snip] > -- > ____________________________________ > William (Bill) Vaughn > Author, Mentor, Consultant > Microsoft MVP > INETA Speaker > www.betav.com/blog/billva > www.betav.com > Please reply only to the newsgroup so that others can benefit. > This posting is provided "AS IS" with no warranties, and confers no rights. > __________________________________ > > "Kerry Moorman" <KerryMoor***@discussions.microsoft.com> wrote in message > news:76AC957F-5F42-4D59-9701-B047DFF8742D@microsoft.com... > > Dino, > > > > What you are trying to do is very nearly impossible using VS.Net and > > ADO.Net. > > > > Most .Net applications handle concurrency issues when a client actually > > attempts to update the database. Why won't that approach work for you? > > > > Kerry Moorman > > > > > > "Dino Buljubasic" wrote: > > > >> Hi, > >> > >> I am using VS2005 (C#) and SQL Server 2000. > >> > >> How can I make sure that: > >> > >> 1. Client A queries info from database and displays it in a list view > >> or other controls on a form. If Client B changes some of this info > >> that is displayed by client A, clint A gets its info updated > >> > >> 2. If clint B tries to delete data currently displayed by client A, > >> the attempt should fail. > >> > >> How can I make sure that database data displayed on the client's forms > >> is always newest data? > >> > >> Any help will be appreciated. > >> > >> _dino_ > >> > > >  |
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