Automatic trigger generator for Django

Create triggers to do some aggregate and permit to count objects from database without using COUNT() aggregat. Detailed documentation is in the "docs" directory.

1. Add "django_aggtrigg" to your INSTALLED_APPS setting like this:

   INSTALLED_APPS = (
       ...
       'django_aggtrigg',
   )

2. Import fields in your models:

   from django_aggtrigg.models import IntegerTriggerField
   from django_aggtrigg.models import FloatTriggerField

3. Configure your fields as is:

   class Apple(models.Model):
       indice = IntegerTriggerField(default=0)
       indice.aggregate_trigger=['count','min']
   
       mark = FloatTriggerField(default=0)
       mark.aggregate_trigger=['min']

By default only the count aggregat will be created.

4. Use the new manager on you Model

   objects = AggTriggManager()

To create the triggers in the database do:

python manage.py aggtrigg_create

Dropping triggers is easy as doing:

python manage.py aggtrigg_drop | psql -d DATABASE NAME

For safety reason the drop command just ouptput on stdout the SQL statements.

To initialize the aggregeate table, you can fill it by hand or do:

python manage.py aggtrigg_initialize

Instead of doing a COUNT as the traditionnal way:

Apple.objects.filter(indice=42).count()

you will do:

Apple.objects.optimized_count(indice=42)

This is may be less easy, but so much more efficient when you manipulate billions or tuples in your relations.

The class apple was create in the app called foo so the default name of the table that contains data will be foo_apple, we use the tablename from the Model so if it's changed in Meta will still be compliant.

A new table foo_apple__indice_agg is created in the same database as foo_apple, it will contain the aggregat:

foo=# \d foo_apple__indice_agg
Table "public.foo_apple__indice_agg"
  Column   |  Type   | Modifiers
-----------+---------+-----------
 indice    | integer |
 agg_count | integer |
 agg_min   | integer |
Indexes:
    "foo_apple__indice_agg_indice_idx" btree (indice)

If you need to maintain count on related objects, for example the comment count per Article, you can use ForeignKeyTriggerField:

from django_aggtrigg.models import ForeignKeyTriggerField

Trade the ForeignKey on ArticleComment for a ForeignKeyTriggerField:

class ArticleComment(models.Model):
    ...
    article = ForeignKeyTriggerField(Article)
    ...

Add simple count:

article.aggregate_trigger = ["count"]

Or complex one with some filters:

article.aggregate_trigger = [{'count': [
                                {'private': [ {
                                    "field": "is_private",
                                    "value": False}
                                             ]
                                 }
                                       ]
                             }]

Create your triggers:

python manage.py aggtrigg_create

Initialize your triggers:

python manage.py aggtrigg_initialize

To use those triggers easily, you can use AggCount manager:

from django_aggtrigg.models import AggCount

ArticleManager = Manager.include(AggCount)

AggCount give you a new method on your model: get_count. You can use it juste like a traditional queryset method. ex:

Article.objects.filter(..).get_count().values("articlecomment_count_private")
[{'ticketcomment_count_private': 4},
{'ticketcomment_count_private': 2},..]

Article.objects.filter(..).get_count().first().__dict__
{'id': 24,
 ...
 'ticketcomment_count_private': 3
 ...}

The only thing you cannot do with get_count is filtering on the aggregates. ex:

Article.objects.get_count().filter(articlecomment_count_private__gte=3)
# THIS DOES NOT WORK !!!

Because the aggregates are not on the table you working on, Django does not really know anything about this table. THis is the reason why you do not have to bother with migrations.