On Sun, Dec 21, 2014 at 12:55 PM, Collin Anderson <cmawebsite@gmail.com> wrote:
Hi Erik,If you want a nicer interface, I just ran manage.py inspecdb on one of my databases and got this for the cache table. Not sure why django still does it by hand.
Gather `round, children, and let Grandpa fill you in on the details... :-)
Although it isn't huge, Django's ORM does have an overhead. If you're looking for the general capability to query rows on a database, this overhead is a reasonable price to pay - you have a little overhead, but it's a lot easier to express complex queries. However, in the case of a cache table, you need to issue exactly 2 queries:
1) Get me the object with key X.
2) Set the value of key X.
These two queries are trivial to write -- so trivial in fact, that they don't even need to rewritten as they move across database backends. They're as "vanilla" as a query can get in SQL.
So - this becomes a case study in when *not* to use the ORM. We know the 2 queries that need to be issued. That SQL isn't hard to write or maintain. And using the ORM would impose a non-trivial runtime overhead - and by definition, a cache backend is supposed to be as efficient as possible. Raw SQL is the "right" answer here.
(well.... not using a database backed cache backend is the *really* right answer, but I'll let that slide for the moment...)
If you *do* want to do complex queries on the database cache table, the approach suggested by Collin is as good an approach as any. A managed table will give you ORM operations over an arbitrary table - include Django's own internal tables.
That said, I'll also concur that the database cache backend is the wrong answer here. If you're writing a cron script, the approach I've always used is PIDfile based lock:
Yours,
Russ Magee %-)
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