It seems that many problems I see in this list revolve around determining
the next record for an insert and methods to use cftransaction as a form of
database locking to achieve this purpose. So, I figured I would add two
cents that might help some of you.
First, what you can do is determined by what product you are using.
Oracle has a nifty little table called DUAL. It's a system table that will
always have only one row. So, if you "Select nextval from Dual" you will
have a unique id you can then store in a variable and use for inserts. If
you use this for all your tables, then your ID values will be different in
all of your tables, an interesting thing to play with in joins or table
merges. No record will ever have the same ID. Beware, I have heard of
resetting the Dual Table. Never had it happen to me.
Access doesn't have any good way to prevent the multiple simultaneous insert
problem. So, by using CFCatch, and CFTransaction you can catch the error of
the second insert, rollback the changes and try again with a new value.
CFTransaction seems to suggest that your set of queries will all run
sequentially and then allow others to access the instance. But, in truth, I
don't think the tables are locked. Surrounding the code with CFLock will
supposedly single thread your server's requests, and if your server has
exclusive access to the datasource, that's great. If others also access
your datasource, then even that won't help you. But, let's get realistic.
If you're using Access, you can achieve a more than reasonable level of
success using CFLock, CFCatch and CFTransaction. (does CFTransaction roll
back in Access, I can't remember)
SQL Server is a bit different. You could use the Access method above with
reasonable success. However, you would be better off to use something like
the following code.
<cfquery name="insertPeople" datasource="#dsn1#">
set nocount on
insert into people
values
('#thepassword#', '#theusername#'')
SELECT lastid = @@identity
set nocount off
</cfquery>
Surround this query with CFLock, CFCatch, and CFTransaction to make it
almost bulletproof. Simply refer to #insertPeople.lastid# in the subsequent
queries wherever you want to sync the new id.
Of course, the very best way to make 100% certain that you are preserving
the ID in SQL server or Oracle is to use a Stored Procedure and lock the
tables while executing the methods above.
Good Fortune,
Rick Walters
Webmaster, Davita Laboratory Services
Office: (800) 604-5227
Cell: (407) 491-9848
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