django-closuretree

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django-closuretree is an implementation of the closure tree <http://homepages.inf.ed.ac.uk/libkin/papers/tc-sql.pdf>_ technique for Django <https://djangoproject.com>_ applications designed to provide efficient querying of tree-based structures <http://en.wikipedia.org/wiki/Tree_%28data_structure%29>_ in a relational database. Its goal is to reduce the number of queries required when querying the children or parents of a given object.

Given the following model:

.. code-block:: python

class Node(models.Model):
    name = models.CharField(max_length=24)
    parent = models.ForeignKey('self', related_name='children')

The children of each model can be queried with:

.. code-block:: python

Node.objects.get(name='A').children.all()

However, for recursive lookups, this results in a large number of queries. Instead, django-closuretree allows you to extract them all in one go:

.. code-block:: python

from closuretree.models import ClosureModel

class Node(ClosureModel):
    name = models.CharField(max_length=24)
    parent = models.ForeignKey('self', related_name='children', null=True)

a = Node.objects.create(name='A')
Node.objects.create(name='B', parent=a)

Node.objects.get(name='A').get_descendants()

A single query will obtain all the descendants.

=========== Quick Start

• Install django-closuretree with pip install django-closuretree.
• Inherit your models from closuretree.models.ClosureModel instead of django.db.models.Model.

That's it. You can now use get_descendants() and get_ancestors() on a model instance.

If you're adding this to an existing application that already has data in the database, you'll need to run the rebuildtable() method of each model before the closure tree will be populated with the existing data:

.. code-block:: python

Node.rebuildtable()

============ Contributing

To contribute, fork the repo, do your work, and issue a pull request. We ask that contributors adhere to PEP8 <https://www.python.org/dev/peps/pep-0008/>_ standards, and include full tests for all their code.