Re: Caching at model class level

Normally this is cached using the Django caching framework, this lets you save it in memcache, redis, etc

On Thursday, November 3, 2011 at 10:22 AM, Thomas Guettler wrote:

Hi,

I try to reduce the number of db-queries in my app.

There is a model which changes almost never. It is like a "type of ticket"

in a trouble ticket system.

On one page there are seven SQL-Queries (SELECT .... FROM ticket_type where id=123) which of course always return

the same result.

I want to cache the objects:

t1=TicketType.objects.get(id=123)

t2=TicketType.objects.get(id=123)

t1 and t2 should be the identical python object, not just objects containing the same data.

Has someone done this before?

Here is my first version:

class ThreadLocalQueryset(models.query.QuerySet):

_threadlocal=threading.local()

_threadlocal.cache=dict() # The cache is at class-level. It survives a request.

def get(self, **kwargs):

kwargs_tuple=tuple(kwargs.items())

obj=self._threadlocal.cache.get(kwargs_tuple)

if obj is not None:

return obj

obj=models.query.QuerySet.get(self, **kwargs)

self._threadlocal.cache[kwargs_tuple]=obj

return obj

class ThreadLocalManager(models.Manager):

use_for_related_fields = True

def get_query_set(self):

return ThreadLocalQueryset(self.model, using=self._db)

class TicketType(models.Model):

objects=ThreadLocalManager()

If there would be many TicketTypes, the interpreter would use more and more memory, but there are few.

Feedback welcome,

Thomas Güttler

--

Thomas Guettler, http://www.thomas-guettler.de/

E-Mail: guettli (*) thomas-guettler + de

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