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Welcome to Maat's documentation!

A Django application that optimizes ordered queryset retrieving when using MySQL.

This is expecially useful when you have to display a list of objects using one or more ordering criteria.

The high speed is due to an external table thoughtfully indexed that optimizes both the join and the ordering of the rows without file sorting.

Specifically, the index is built in a way that all the columns in the WHERE clause are constant.

Further documentation can be found here: http://dev.mysql.com/doc/refman/5.0/en/order-by-optimization.html

Requirements

Python 2 > 2.7
Python 3 >= 3.4
Django >= 1.8

Contents

.. toctree::
   :maxdepth: 2

   changelog


Installation

Install the djangomaat package:

pip install djangomaat

Make sure djangomaat is listed among your INSTALLED_APPS:

INSTALLED_APPS = [
    # [...]
    'djangomaat',
]

Run the syncdb command, or migrate if you are using Django 1.7:

./manage.py syncdb

Usage

In order to use Maat, you need to create a subclass of MaatHandler for each Django model you want to use and attach it to it.

This class expects one or more methods whose name starts with get_pk_list_for_.

The suffix you will append to the name of the method will be used to retrieve the objects from the original model (more on this later).

Each of these methods must return a list of pks (or an iterator, which is actually preferable) in the same order they are expected to be returned. Note that nothing forces you to returns the whole list of instances of the model. You can returns a subset if that is what you need.

from djangomaat.register import maat
from djangomaat.handlers import MaatHandler

class ArticleMaatHanlder(MaatHandler):

    def get_pk_list_for_comment_count(self):
        return Article.objects.filter(
            thread__content_type=ContentType.objects.get_for_model(Article),
        ).order_by('-thread__comment_count').values_list('pk', flat=True)[:1000].iterator()

    def get_pk_list_for_popularity(self):
        return Article.objects.filter(
            popularity__content_type=ContentType.objects.get_for_model(Article),
        ).order_by('-popularity__score').values_list('pk', flat=True)[:1000].iterator()

maat.register(Article, ArticleMaatHanlder)

In the example above, we have two methods because we want to list the most commented and the most popular articles (only the first thousand of them).

After that, remember to register your handler as shown on the last line.

Note

In Django 1.6 the preferred module for this code to live in is the models.py of your application, as it gets imported automatically.

If you are using Django > 1.7 you might want to use AppConfig.ready() instead.

Now that you are done defining your subclasses, you need to tell Maat to built its index:

./manage.py populate_maat_ranking

This will, as a matter of fact, denormalize the current order of the objects.

Now you can finally retrieve your objects, for example in a Django view, using a maat handler that is automatically attached to the model class:

most_popular_articles = Article.maat.ordered_by('popularity')
most_commented_articles = Article.maat.ordered_by('comment_count')

You can also retrieve them in inverted order:

less_popular_article = Article.maat.ordered_by('-popularity')
less_commented_article = Article.maat.ordered_by('-comment_count')

Important: the order of the objects is frozen at the time you run populate_maat_ranking. Depending on your requirements, you should schedule the command to run at regular intervals.

If you need to have different intervals for different models, you can pass a list of app_label.model_name:

./manage.py populate_maat_ranking my_app.article

This will rebuild only the handler registered for that particular model.

Moreover, you can rebuild only given sorting function with the following syntax:

./manage.py populate_maat_ranking my_app.article:popularity,comment_count

That is, add a comma separated values after a colon with the name of your sorting criteria.