John,
You need to decide how you want to handle concurrency issues in a particular
application.
For example, how do you want to handle this situation:
Mary loads your employee record from the Employees table into the Employee
Manager application. She loaded your record because your cell phone number
has changed and she is updating that piece of information in your record.
While Mary is working on your record, Jim loads your employee record from
the Employees table into the Employee Manager application. He loaded your
record because you have just gotten a big raise and he is updating that piece
of information in your record. He changes your salary and updates your record
in the database.
Mary has now finished changing your cell phone number and attempts to update
your record in the database.
Do you want Mary's update to succeed? If it does you have just lost your
raise because her update will overwrite your new salary that Jim entered with
your old salary as it was when Mary loaded your record.
Do you want Mary's update to fail because of a concurrency conflict? When it
fails, how do you want to deal with the conflict?
Your current code appears to read the updated record and then apply the old
values to it. This gets rid of the concurrency conflict but you still end up
with your old salary instead of your raise.
My choice would be to inform the user that the record has been changed by
another user and let the user reload the record and start over.
Kerry Moorman
"John" wrote:
So Kerry how do I handle it? which was my original question.
Regards
"Kerry Moorman" <Ke**********@discussions.microsoft.comwrote in message
news:31**********************************@microsof t.com...
John,
It looks like your approach to concurrency handling is to get around the
concurrency error by reloading the data from the database and then
applying
your changes.
You might as well just turn off concurrency checking, since that is the
end
result anyway.
In other words, it looks like your code is just avoiding concurrency
exceptions, not handling concurrency conflicts.
Kerry Moorman
"John" wrote:
Hi
I have developed the following logic to handle db concurrency violations.
I
just wonder if someone can tell me if it is correct or if I need a
different approach.Would love to know how pros handle it.
Thanks
Regards
Dim dc As DataColumn
Dim drCache As DataRow
Dim drCurrent As DataRow
Try
' Attempt the update
daContacts.Update(ds.Contacts)
Catch Ex As DBConcurrencyException
' First - cache the row
drCache = ds.Contacts.NewRow()
For Each dc In ds.Contacts.Columns
If Not dc.ReadOnly Then
drCache(dc.ColumnName) = Ex.Row(dc.ColumnName)
End If
Next
' Refresh from database
daContacts.Fill(ds.Contacts)
' Position to the faulted row
drCurrent = ds.Contacts.Rows.Find(Ex.Row("ID"))
' Apply User Changes
For Each dc In ds.Contacts.Columns
If Not dc.ReadOnly Then
drCurrent(dc.ColumnName) = drCache(dc.ColumnName)
End If
Next
' Save again
daContacts.Update(ds.Contacts)
End Try
