Cloud Spanner support for Django
================================

|GA| |pypi| |versions|

`Cloud Spanner`_ is the world's first fully managed relational database service
to offer both strong consistency and horizontal scalability for
mission-critical online transaction processing (OLTP) applications. With Cloud
Spanner you enjoy all the traditional benefits of a relational database; but
unlike any other relational database service, Cloud Spanner scales horizontally
to hundreds or thousands of servers to handle the biggest transactional
workloads.


- `Client Library Documentation`_
- `Product Documentation`_

.. |GA| image:: https://img.shields.io/badge/support-GA-gold.svg
   :target: https://github.com/googleapis/google-cloud-python/blob/main/README.rst#general-availability
.. |pypi| image:: https://img.shields.io/pypi/v/django-google-spanner.svg
   :target: https://pypi.org/project/django-google-spanner/
.. |versions| image:: https://img.shields.io/pypi/pyversions/django-google-spanner.svg
   :target: https://pypi.org/project/django-google-spanner/
.. _Cloud Spanner: https://cloud.google.com/spanner/
.. _Client Library Documentation: https://googleapis.dev/python/django-google-spanner/latest/index.html
.. _Product Documentation:  https://cloud.google.com/spanner/docs

Quick Start
-----------

In order to use this library, you first need to go through the following steps:

1. `Select or create a Cloud Platform project.`_
2. `Enable billing for your project.`_
3. `Enable the Google Cloud Spanner API.`_
4. `Setup Authentication.`_

.. _Select or create a Cloud Platform project.: https://console.cloud.google.com/project
.. _Enable billing for your project.: https://cloud.google.com/billing/docs/how-to/modify-project#enable_billing_for_a_project
.. _Enable the Google Cloud Spanner API.:  https://cloud.google.com/spanner
.. _Setup Authentication.: https://googleapis.dev/python/google-api-core/latest/auth.html

This package provides a `3rd-party database backend
<https://docs.djangoproject.com/en/2.2/ref/databases/#using-a-3rd-party-database-backend>`__
for using `Cloud Spanner <https://cloud.google.com/spanner>`__ with the `Django
ORM <https://docs.djangoproject.com/en/2.2/topics/db/>`__. It uses the `Cloud
Spanner Python client library <https://github.com/googleapis/python-spanner>`__
under the hood.

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

Install this library in a `virtualenv`_ using pip. `virtualenv`_ is a tool to
create isolated Python and Django environments. The basic problem it addresses is one of
dependencies and versions, and indirectly permissions.

With `virtualenv`_, it's possible to install this library without needing system
install permissions, and without clashing with the installed system
dependencies.

.. _`virtualenv`: https://virtualenv.pypa.io/en/latest/


Supported versions
~~~~~~~~~~~~~~~~~~

The library supports `Django 2.2
<https://docs.djangoproject.com/en/2.2/>`_, and `Django 3.2
<https://docs.djangoproject.com/en/3.2/>`_.
Both versions are long-term support (LTS) releases for the
`Django project<https://www.djangoproject.com/download/#supported-versions>_`.
The minimum required Python version is 3.6.

.. code:: shell

    pip3 install django==3.2


Installing the package
~~~~~~~~~~~~~~~~~~~~~~

To install from PyPI:

.. code:: shell

    pip3 install django-google-spanner


To install from source:

.. code:: shell

    git clone git@github.com:googleapis/python-spanner-django.git
    cd python-spanner-django
    pip3 install -e .


Creating a Cloud Spanner instance and database
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you don't already have a Cloud Spanner database, or want to start from
scratch for a new Django application, you can `create a new instance
<https://cloud.google.com/spanner/docs/getting-started/python#create_an_instance>`__
and `database
<https://cloud.google.com/spanner/docs/getting-started/python#create_a_database>`__
using the Google Cloud SDK:

.. code:: shell

    gcloud spanner instances create $INSTANCE --config=regional-us-central1 --description="New Django Instance" --nodes=1
    gcloud spanner databases create $DB --instance $INSTANCE


Configuring ``settings.py``
~~~~~~~~~~~~~~~~~~~~~~~~~~~

This package provides a Django application named ``django_spanner``. To use the
Cloud Spanner database backend, the application needs to installed and
configured:

-  Add ``django_spanner`` as the first entry in ``INSTALLED_APPS``:

   .. code:: python

       INSTALLED_APPS = [
           'django_spanner',
           ...
       ]

-  Edit the ``DATABASES`` setting to point to an existing Cloud Spanner database:

   .. code:: python

       DATABASES = {
           'default': {
               'ENGINE': 'django_spanner',
               'PROJECT': '$PROJECT',
               'INSTANCE': '$INSTANCE',
               'NAME': '$DATABASE',
           }
       }

  Transaction support in autocommit mode
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  Django version 4.2 and higher by default supports transactions in autocommit mode.
  A transaction is automatically started if you define an
  [atomic block](https://docs.djangoproject.com/en/4.2/topics/db/transactions/#controlling-transactions-explicitly).
  
  Django version 3.2 and earlier did not support transactions in autocommit mode with Spanner.
  You can enable transactions in autocommit mode with Spanner with the
  `ALLOW_TRANSACTIONS_IN_AUTO_COMMIT` configuration option.

  - To enable transactions in autocommit mode in V3.2, set
  the flag "ALLOW_TRANSACTIONS_IN_AUTO_COMMIT" to True in your
  settings.py file.
  - To disable transactions in autocommit mode in V4.2, set
  the flag "ALLOW_TRANSACTIONS_IN_AUTO_COMMIT" to False in your
  settings.py file.


Set credentials and project environment variables
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
You'll need to download a service account JSON key file and point to it using an environment variable:

.. code:: shell

    export GOOGLE_APPLICATION_CREDENTIALS=/path/to/keyfile.json
    export GOOGLE_CLOUD_PROJECT=gcloud_project


Apply the migrations
~~~~~~~~~~~~~~~~~~~~

Please run:

.. code:: shell

    $ python3 manage.py migrate

That'll take a while to run. After this you should be able to see the tables and indexes created in your Cloud Spanner console.


Create a Django admin user
~~~~~~~~~~~~~~~~~~~~~~~~~~~
First you’ll need to create a user who can login to the admin site. Run the following command:

.. code:: shell

    $ python3 manage.py createsuperuser

which will then produce a prompt which will allow you to create your super user

.. code:: shell

    Username: admin
    Email address: admin@example.com
    Password: **********
    Password (again): **********
    Superuser created successfully.


Login as admin
~~~~~~~~~~~~~~
Now, run the server

.. code:: shell

    python3 manage.py runserver

Then visit http://127.0.0.1:8000/admin/

Create and register your first model
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Please follow the guides in https://docs.djangoproject.com/en/2.2/intro/tutorial02/#creating-models
to create and register the model to the Django’s automatically-generated admin site.

How it works
------------

Overall design
~~~~~~~~~~~~~~

.. figure:: https://raw.githubusercontent.com/googleapis/python-spanner-django/main/assets/overview.png
   :alt: "Overall Design"

Internals
~~~~~~~~~

.. figure:: https://raw.githubusercontent.com/googleapis/python-spanner-django/main/assets/internals.png
   :alt: "Internals"


Executing a query
~~~~~~~~~~~~~~~~~

Here is an example of how to add a row for Model Author, save it and later query it using Django

.. code:: shell

    >>> author_kent = Author( first_name="Arthur", last_name="Kent", rating=Decimal("4.1"),)
    >>> author_kent.save()
    >>> qs1 = Author.objects.all().values("first_name", "last_name")


How to contribute
~~~~~~~~~~~~~~~~~

Contributions to this library are always welcome and highly encouraged.

See `CONTRIBUTING <https://github.com/googleapis/python-spanner-django/blob/main/CONTRIBUTING.md>`_ for more information on how to get started.

Please note that this project is released with a Contributor Code of Conduct.
By participating in this project you agree to abide by its terms. See the `Code 
of Conduct <https://github.com/googleapis/python-spanner-django/blob/main/CODE_OF_CONDUCT.md>`_ for more information.


Limitations
~~~~~~~~~~~

Spanner has certain limitations of its own. The full set of limitations is documented
`here <https://cloud.google.com/spanner/quotas#schema_limits>`__.
It is recommended that you go through that list.

Django spanner has a set of limitations as well, which you can find
`here <https://github.com/googleapis/python-spanner-django/blob/main/docs/limitations.rst>`__.

Features from spanner that are not supported in Django-spanner are listed 
`here <https://github.com/googleapis/python-spanner-django/blob/main/docs/limitations-spanner.rst>`__.