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Create and manage Postgres SQL Views in Django

Project description

SQL Views for Postgres
======================

|Gitter| |Circle CI|

Adds first-class support for `PostgreSQL
Views <http://www.postgresql.org/docs/9.1/static/sql-createview.html>`__
in the Django ORM

Installation
------------

Install via pip:

::

pip install django-pgviews

Add to installed applications in settings.py:

.. code:: python

INSTALLED_APPS = (
# ...
'django_pgviews',
)

Examples
--------

.. code:: python

from django.db import models

from django_pgviews import view as pg


class Customer(models.Model):
name = models.CharField(max_length=100)
post_code = models.CharField(max_length=20)
is_preferred = models.BooleanField(default=False)

class Meta:
app_label = 'myapp'

class PreferredCustomer(pg.View):
projection = ['myapp.Customer.*',]
dependencies = ['myapp.OtherView',]
sql = """SELECT * FROM myapp_customer WHERE is_preferred = TRUE;"""

class Meta:
app_label = 'myapp'
db_table = 'myapp_preferredcustomer'
managed = False

**NOTE** It is important that we include the ``managed = False`` in the
``Meta`` so Django 1.7 migrations don't attempt to create DB tables for
this view.

The SQL produced by this might look like:

.. code:: postgresql

CREATE VIEW myapp_preferredcustomer AS
SELECT * FROM myapp_customer WHERE is_preferred = TRUE;

To create all your views, run ``python manage.py sync_pgviews``

You can also specify field names, which will map onto fields in your
View:

.. code:: python

from django_pgviews import view as pg


VIEW_SQL = """
SELECT name, post_code FROM myapp_customer WHERE is_preferred = TRUE
"""


class PreferredCustomer(pg.View):
name = models.CharField(max_length=100)
post_code = models.CharField(max_length=20)

sql = VIEW_SQL

Features
--------

Updating Views
~~~~~~~~~~~~~~

Sometimes your models change and you need your Database Views to reflect
the new data. Updating the View logic is as simple as modifying the
underlying SQL and running:

::

python manage.py sync_pgviews --force

This will forcibly update any views that conflict with your new SQL.

Dependencies
~~~~~~~~~~~~

You can specify other views you depend on. This ensures the other views
are installed beforehand. Using dependencies also ensures that your
views get refreshed correctly when using ``sync_pgviews --force``.

**Note:** Views are synced after the Django application has migrated and
adding models to the dependency list will cause syncing to fail.

Example:

.. code:: python

from django_pgviews import view as pg

class PreferredCustomer(pg.View):
dependencies = ['myapp.OtherView',]
sql = """SELECT * FROM myapp_customer WHERE is_preferred = TRUE;"""

class Meta:
app_label = 'myapp'
db_table = 'myapp_preferredcustomer'
managed = False

Materialized Views
~~~~~~~~~~~~~~~~~~

Postgres 9.3 and up supports `materialized
views <http://www.postgresql.org/docs/current/static/sql-creatematerializedview.html>`__
which allow you to cache the results of views, potentially allowing them
to load faster.

However, you do need to manually refresh the view. To do this
automatically, you can attach
`signals <https://docs.djangoproject.com/en/1.8/ref/signals/>`__ and
call the refresh function.

Example:

.. code:: python

from django_pgviews import view as pg


VIEW_SQL = """
SELECT name, post_code FROM myapp_customer WHERE is_preferred = TRUE
"""

class Customer(models.Model):
name = models.CharField(max_length=100)
post_code = models.CharField(max_length=20)
is_preferred = models.BooleanField(default=True)


class PreferredCustomer(pg.MaterializedView):
name = models.CharField(max_length=100)
post_code = models.CharField(max_length=20)

sql = VIEW_SQL


@receiver(post_save, sender=Customer)
def customer_saved(sender, action=None, instance=None, **kwargs):
PreferredCustomer.refresh()

Postgres 9.4 and up allow materialized views to be refreshed
concurrently, without blocking reads, as long as a unique index exists
on the materialized view. To enable concurrent refresh, specify the name
of a column that can be used as a unique index on the materialized view.
Once enabled, passing ``concurrently=True`` to the model's refresh
method will result in postgres performing the refresh concurrently.
(Note that the refresh method itself blocks until the refresh is
complete; concurrent refresh is most useful when materialized views are
updated in another process or thread.)

Example:

.. code:: python

from django_pgviews import view as pg


VIEW_SQL = """
SELECT id, name, post_code FROM myapp_customer WHERE is_preferred = TRUE
"""

class PreferredCustomer(pg.MaterializedView):
concurrent_index = 'id'
sql = VIEW_SQL

name = models.CharField(max_length=100)
post_code = models.CharField(max_length=20)


@receiver(post_save, sender=Customer)
def customer_saved(sender, action=None, instance=None, **kwargs):
PreferredCustomer.refresh(concurrently=True)

Custom Schema
~~~~~~~~~~~~~

You can define any table name you wish for your views. They can even
live inside your own custom `PostgreSQL
schema <http://www.postgresql.org/docs/current/static/ddl-schemas.html>`__.

.. code:: python

from django_pgviews import view as pg


class PreferredCustomer(pg.View):
sql = """SELECT * FROM myapp_customer WHERE is_preferred = TRUE;"""

class Meta:
db_table = 'my_custom_schema.preferredcustomer'
managed = False

Django Compatibility
--------------------

.. raw:: html

<table>

.. raw:: html

<thead>

::

<tr>
<th>Django Version</th>
<th>Django-PGView Version</th>
</tr>

.. raw:: html

</thead>

.. raw:: html

<tbody>

::

<tr>
<td>1.4 and down</td>
<td>Unsupported</td>
</tr>
<tr>
<td>1.5</td>
<td>0.0.1</td>
</tr>
<tr>
<td>1.6</td>
<td>0.0.3</td>
</tr>
<tr>
<td>1.7</td>
<td>0.0.4</td>
</tr>
<tr>
<td>1.9</td>
<td>0.1.0</td>
</tr>
<tr>
<td>1.10</td>
<td>0.2.0</td>
</tr>

.. raw:: html

</tbody>

.. raw:: html

</table>

Django 1.7 Note
~~~~~~~~~~~~~~~

Django 1.7 changed how models are loaded so that it's no longer possible
to do ``sql = str(User.objects.all().query)`` because the dependent
models aren't yet loaded by Django.

Django 1.9 Note
~~~~~~~~~~~~~~~

You now have to use the ``.view`` module directly.

Python 3 Support
----------------

Django PGViews supports Python 3 in versions 0.0.7 and above.

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