> Hi, in VB.NET I'm accessing a DBF file using ADO with an OLEDB connection
> with the Visual Foxpro OLEDB driver (VFPODBC.DLL).  Read, write, update,
> delete all work fine using a dataset.
> Is there any automatic way to handle concurrent updates to the same record
> by different users.  How would it work?   If I had to do it manually I'd
> use
> a "last updated" timestamp and do something like this:
>
> step 1. Read record without lock
> step 2. modify record
> step 3. read same record with lock
> step 4. compare last updated timestamps
> step 5. If they match then write the record and release lock
> step 6. if they don't match then release record lock and disp error msg to
> user
>
> If I did this manually, I still don't know how to do a "read with record
> lock" to protect the record during that small window between steps 3 and
> 5.
>
> Right now I'm using a dataset to do the update/delete/insert operations
> then
> updating the database with a DataAdapter.Update method.  I'm open to using
> another technique if it's required to protect the records from concurrent
> updates.
>
> I heard about something called "pessimistic locking" and "optimistic
> locking" (or something like
> that).  Would that apply to my case?  If so how would it work?
>
> I can't imagine this is an unusual requirement... I've never had a problem
> figuring out
> record locking in any other programming environment...  .NET is very
> powerful, but
> it seems like some of what should be easy things, are not very obvious!
>
> Thanks, John
>
>
>

> .......
> Is there any automatic way to handle concurrent updates to the same record
> by different users.  How would it work?   ..........

> I heard about something called "pessimistic locking" and "optimistic
> locking" (or something like
> that).  Would that apply to my case?  If so how would it work? .....

"Cindy Winegarden" <cindy_winegar***@msn.com> wrote in message
news:%23YKwRhKNFHA.1176@TK2MSFTNGP12.phx.gbl...
> Hi John,
>
> I don't have time to play with this right now, but you can wrap your
> update in a Transaction and within the Transaction you could do all your
> checking. I answered a question about Transactions recently; you can read
> it at
> http://groups-beta.google.com/group/microsoft.public.dotnet.datatools/browse_frm/thread/be1e5a8924f9247b/c7946cd42abf9a96.
>
> As for optimistic and pessimistic locking, if you're referring to those
> terms in Visual FoxPro, then pessimistic locking locks a record from the
> time you access it until the time you release it, and optimistic locking
> only locks the record when it is actually being written. In this case, if
> another user has modified the record between the time you accessed it and
> the time you actually wrote your changes, then "the last guy wins" as far
> as which updates are retained in the end.
>
> The VFP documentation says that the VFP OLE DB data provider supports the
> standard DBPROP_LOCKMODE  and DBPROP_LOCKMODES properties. Sorry to say I
> haven't ever worked with those.
>
> This is an interesting question - now you've got me curious to learn
> exactly how it all works.
>
> --
> Cindy Winegarden  MCSD, Microsoft Visual Foxpro MVP
> cindy_winegar***@msn.com  www.cindywinegarden.com
> Blog: http://spaces.msn.com/members/cindywinegarden
>
>
> "JohnR" <JohnR***@hotmail.com> wrote in message
> news:GMK1e.23193$Ue6.14492@trndny04...
>> .......
>> Is there any automatic way to handle concurrent updates to the same
>> record
>> by different users.  How would it work?   ..........
>
>> I heard about something called "pessimistic locking" and "optimistic
>> locking" (or something like
>> that).  Would that apply to my case?  If so how would it work? .....
>
>