// off-topic for NHib, but might be interesting ...
> I personally don't understand why people try to use guid PKs everywhere
...
> They might be appropriate
> in some cases (maybe you have some data that needs to interface with a
> external system?) but don't use them in all of your tables!
We used them everywhere. Why? In our scenario, we sell a software to many small
companies (thousands) with their own installations and must live with the fact
that LATER, any two of the databases are going to exchange records (ANY records
- we do not know today which data need to be exchanged one year in the future).
So we need world-wide unique identifiers from the outset.
Moreover, we want (from experience) to be able to (rarely, but still ...)
switch from "table-per-concrete-class" to "table-per-hierarchy", so we also
need database-wide (well, actually "inheritance-tree-wide", but that's hard to
enforce) unique identifiers.
Guids with NEWID() did all that out of the box.
> I wouldn't think twice about getting rid of them.
Still, we painfully accepted that guids are large and clumsy. We are in the
process of going to bigints, but this requires a massive infrastructure that
provides unique ids to the installations ("system ids"); and these ids form now
part of the bigint PK. Some research had to go into the sizes of the "system
id" part vs. the "local object id".
One interesting aspect: For testability and development, we can build a system
with a few commands. So, a typical developer "builds" 10...20 systems per day;
and in unit test suites, many more are built. Therefore, the system ids
required are not thousands (number of our customers), but something like 10000
per day = millions over the years. The infrastructure therefore can distinguish
"short-lived systems" from "lasting systems" and can reuse system ids of the
former ones.
Yet, from a business perspective, GUIDs ("globally unique ..."!!) seem like the
right choice to our problem ...
So much for a story from the trenches ...
Regards
Harald M.
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