Re: 4D Field Incrementing

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2 total messages Started by Graydon Patterson Sun, 24 Jan 1993 02:06

#652

Author: Graydon Patterson
Date: Sun, 24 Jan 1993 02:06

15 lines
836 bytes

Here is the standard procedure I use to create unique ID's..
`	NextID
$0:=[NextID]ID
[NextID]ID:=[NextID]ID+1
SAVE RECORD([NextID])
`    end script

To obtain a unique ID in any file use the following...
[Clients]Client Number:=NextID    ` NEXTID being a function

The NextIF file has only one field called ID and only one
record, the next ID to be called.
(pardon my typos)
--

Re: 4D Field Incrementing

#653

Author: Erik Oliver
Date: Sun, 24 Jan 1993 13:59

32 lines
1674 bytes

In article <1993Jan24.020602.20467@freenet.carleton.ca> aa192@Freenet.carleton.ca (Graydon Patterson) writes:
>
>Here is the standard procedure I use to create unique ID's..
>`	NextID
>$0:=[NextID]ID
>[NextID]ID:=[NextID]ID+1
>SAVE RECORD([NextID])
>`    end script
>
>To obtain a unique ID in any file use the following...
>[Clients]Client Number:=NextID    ` NEXTID being a function
>
>The NextIF file has only one field called ID and only one
>record, the next ID to be called.
>(pardon my typos)
>-- 
>

NO NO NO NO NO.  What if this was a multi-user database, what if lots of
people all over the world tried to get a new ID simultaneously, two
people might both assing $0 := [NextID]ID, and both might get the exact
same value before raising the value of [NextID]ID, in Comp. Sci. terms,
you have a _race condition_.

If you feel the need to use this solution, turn this procedure into a
TRANSACTION, or use the SEMAPHORE features of 4D to protect against this
happening.

But, if you really need Unique IDs, NEVER NEVER NEVER use the above
procedure in a multi-user database, or even in a single user databse

-Erik

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