django-db-views

How to install?

• pip install django-db-views

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_views.db_view import DBView
   
   class Balance(DBView):
  
       virtual_card = models.ForeignKey(
           VirtualCard, 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
           db_table = 'virtual_card_balance'
  

• The view definition must be a string or a callable.

  Callable view definition example:

    view_definition = lambda: str(SomeModel.objects.all().query)
  

  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

As of version 0.1.0 you can also define view_definition as a dict for multiple engine types. This becomes useful if you use a different engine for local / dev / staging / production. 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.settings Example as a dict:

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
    """,
}

Tested with live projects based on Django: 1.11.5, 2.2.10

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