An identity mapper for the Django ORM
An identity mapper for the Django ORM. This is a fork of django-idmapper, which is no longer maintained.
What is it?
django-idmap is a Django application which: - loads only once the instances in memory the first time they are needed - share them througout your interpreter until the request is finished
Indeed, the default django behavior is to expose different instances for the same database entry between the start and the end of the request. It has one main consequence: the temporary attributes you may set are lost if you want to access the same database object in another place in your code.
As straightforward as it can be, using pip:
pip install django-idmap
You then need to add 'idmap' to your INSTALLED_APPS.
To use the exposed shared memory model you simply need to inherit from it (instead of models.Model). This enable all queries (and relational queries) to this model to use the shared memory instance cache, effectively creating a single instance for each unique row (based on primary key) in the queryset.
You can chose between 2 caching modes:
Weak references mode: the instance will be removed from the cache once there are no more references to it. This is the default behavior
Strong references mode: the instance will only be removed from the cache when it is flushed
Note that django-idmap clears the cache when the request_finished or post_syncdb signal is sent. This default behavior can be modified by disconnecting the exposed idmap.flush_cache function from these signals.
You can import idmap.models as you would import django.db.models. idmap.models exposes all what is exposed by django.db.models plus the SharedMemoryModel model class.
You may mix and match SharedMemoryModels with regular Models:
from idmap import models class MyModel(models.SharedMemoryModel): name = models.CharField(...) fkey = models.ForeignKey('Other') class Other(models.Model): name = models.CharField(...)
If you want to use strong references for a particular model, simply set use_strong_refs to True in the derived model class Meta options:
from idmap import models class MyModel(models.SharedMemoryModel): class Meta: use_strong_refs = True [...]
With strong references, the model will be loaded only once from the database, until it is explicitly erased from the cache.
You may want to use the functions or class methods:
idmap.flush_cache() to erase the whole cache
SharedMemoryModel.flush_instance_cache() to erase the cache for one model
SharedMemoryModel.flush_cached_instance(instance) to erase one instance from the cache
D Cramer’s django-idmapper
Original code and concept: http://code.djangoproject.com/ticket/17
Release history Release notifications | RSS feed
Download the file for your platform. If you're not sure which to choose, learn more about installing packages.