django-db-views

django-db-views

Django Versions 2.2 to 4.2+
Python Versions 3.9 to 3.11

How to install?

• pip install django-db-views

What we offer

• Database views
• Materialized views
• views schema migrations
• indexing for materialized views (future)
• database table function (future)

How to use?

• add django_db_views to INSTALLED_APPS
• use makeviewmigrations command to create migrations for view models

How to create view in your database?

• To create your view use DBView class, remember to set view definition attribute.

   from django.db import models
   from django_db_views.db_view import DBView
   
   
   class VirtualCard(models.Model):
       ...
   
   
   class Balance(DBView):
  
       virtual_card = models.ForeignKey(
           VirtualCard,  # VirtualCard is a regular Django model. 
           on_delete=models.DO_NOTHING, related_name='virtual_cards'
       )
       total_discount = models.DecimalField(max_digits=12, decimal_places=2)
       total_returns = models.DecimalField(max_digits=12, decimal_places=2)
       balance = models.DecimalField(max_digits=12, decimal_places=2)
       
       view_definition = """
           SELECT
               row_number() over () as id,  # Django requires column called id
               virtual_card.id as virtual_card_id,
               sum(...) as total_discount,
           ...
       """
   
       class Meta:
           managed = False  # Managed must be set to False!
           db_table = 'virtual_card_balance'
  

• The view definition can be: str/dict or a callable which returns str/dict.

  Callable view definition examples:

   from django_db_views.db_view import DBViewl
  
   class ExampleView(DBView):
       @staticmethod
       def view_definition():
           #  Note for MySQL users:
           #    In the case of MySQL you might have to use: 
           #    connection.cursor().mogrify(*queryset.query.sql_with_params()).decode() instead of str method to get valid sql statement from Query.
           return str(SomeModel.objects.all().query)  
  
       # OR
       view_definition = lambda: str(SomeModel.objects.all().query)
       class Meta:
           managed = False 
           db_table = 'example_view'
  

  using callable allow you to write view definition using ORM.

• Ensure that you include managed = False in the DBView model's Meta class to prevent Django creating it's own migration.

How view migrations work?

• DBView working as regular django model. You can use it in any query.
• It's using Django code, view-migrations looks like regular migrations.
• It relies on db_table names.
• makeviewmigrations command finds previous migration for view.
  • if there is no such migration then script create a new migration
  • if previous migration exists but no change in view_definition is detected nothing is done
  • if previous migration exists, then script will use previous view_definition for backward operation, and creates new migration.
  • when run it will check if the current default engine definined in django.settings is the same engine the view was defined with

Multidatabase support

Yoy can define view_definition as a dict for multiple engine types.

If you do not pass in an engine and have a str or callable the engine will be defaulted to the default database defined in django.

It respects --database flag in the migrate command, So you are able to define a specific view definitions for specific databases using the engine key. If the key do not match your current database, view migration will be skipped.

Also, feature becomes useful if you use a different engine for local / dev / staging / production.

Example dict view definition:

view_definition = {
    "django.db.backends.sqlite3": """
        SELECT
            row_number() over () as id,
            q.id as question_id,
            count(*) as total_choices
        FROM question q
        JOIN choice c on c.question_id = q.id
        GROUP BY q.id
    """,
    "django.db.backends.postgresql": """
        SELECT
            row_number() over () as id,
            q.id as question_id,
            count(*) as total_choices
        FROM question q
        JOIN choice c on c.question_id = q.id
        GROUP BY q.id
    """,
}

Materialized Views

Just inherit from DBMaterializedView instead of regular DBView

Materialzied View provide an extra class method to refresh view called refresh

Notes

Please use the newest version. version 0.1.0 has backward incompatibility which is solved in version 0.1.1 and higher.