--- On Fri, 11/20/09, Conor <[email protected]> wrote:
>
> Also, there is a recipe that looks for a matching object in
> the session
> before querying the database:
> http://www.sqlalchemy.org/trac/wiki/UsageRecipes/UniqueObject
>
> -Conor
>
Thank you Conor for you useful pointer. I have used this recipe and changed a
little bit to use beaker as a caching mechanism with a memcached backend. So
here's how it looks like :
from elixir import Entity, EntityMeta,setup_all,create_all,metadata
from pylons import cache
class MetaTag(EntityMeta):
cache = cache.get_cache("tags",type="memory")
def __call__(cls,name):
"""
If it's in the cache, return the cached version
If not in the cache :
If it's in the database, retrieve it, cache it and return it
If it's not there, create it, cache it and return it
"""
theTag = MetaTag.cache.get_value(key=name,createfunc=lambda:None)
if not theTag :
#not in the cache
theTag = cls.query.filter_by(name=name).first()
if not theTag:
#not in the database either
print "not in the database"
theTag = type.__call__(cls,name)
session.add(theTag)
#Adding it to the cache, after creating it in the database if it
wasn't there
MetaTag.cache.set_value(key=name,value=theTag)
return theTag
class Tag(Entity):
__metaclass__ = MetaTag
using_options (tablename="Tags")
name = Field(Unicode(64))
def __init__(self,name,*args,**kw):
Entity.__init__(self,*args,**kw)
self.name = name
def __repr__(self):
return "<Tag %s>" % self.name
metadata.bind = "mysql://username:passw...@localhost:3306/db"
metadata.bind.echo = True
setup_all()
create_all()
And here's how it plays on the interpreter (ipython) :
Alger is already in the database, Constantine is not. I find the metaclass
approach very API-friendly.
...
In [4]: Tag("Alger")
21:38:21,328 INFO [sqlalchemy.engine.base.Engine.0x...2fec] BEGIN
/home/chaouche/PYTHONENV/lib/python2.6/site-packages/SQLAlchemy-0.5.5-py2.6.egg/sqlalchemy/engine/default.py:230:
SAWarning: Unicode type received non-unicode bind param value 'Alger'
param.append(processors[key](compiled_params[key]))
21:38:21,382 INFO [sqlalchemy.engine.base.Engine.0x...2fec] SELECT `Tags`.id
AS `Tags_id`, `Tags`.name AS `Tags_name`
FROM `Tags`
WHERE `Tags`.name = %s
LIMIT 0, 1
21:38:21,382 INFO [sqlalchemy.engine.base.Engine.0x...2fec] ['Alger']
Out[4]: <Tag Alger>
In [5]: Tag("Alger")
Out[5]: <Tag Alger>
In [8]: Tag("Constantine")
/home/chaouche/PYTHONENV/lib/python2.6/site-packages/SQLAlchemy-0.5.5-py2.6.egg/sqlalchemy/engine/default.py:230:
SAWarning: Unicode type received non-unicode bind param value 'Constantine'
param.append(processors[key](compiled_params[key]))
21:39:17,487 INFO [sqlalchemy.engine.base.Engine.0x...2fec] SELECT `Tags`.id
AS `Tags_id`, `Tags`.name AS `Tags_name`
FROM `Tags`
WHERE `Tags`.name = %s
LIMIT 0, 1
21:39:17,487 INFO [sqlalchemy.engine.base.Engine.0x...2fec] ['Constantine']
not in the database
Out[8]: <Tag Constantine>
In [9]: Tag("Constantine")
Out[9]: <Tag Constantine>
Any comments are very appreciated.
Y.Chaouche
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=.
