ORM plugin for using Cloud Spanner as a database backend for Django.
To use this library you'll need a Google Cloud Platform project with the Cloud Spanner API enabled. See the Cloud Spanner Python client docs for details.
Use the version of python-spanner-django
that corresponds to your version of Django. For example, python-spanner-django
2.2.x works with Django 2.2.y. (This is the only supported version at this time.)
The minor release number of Django doesn't correspond to the minor release number of python-spanner-django
. Use the latest minor release of each.
To install from PyPI:
pip3 install django-google-spanner
To install from source:
git clone git@github.com:googleapis/python-spanner-django.git
cd python-spanner-django
pip3 install -e .
After installation, you'll need to edit your Django settings.py
file:
Add
django_spanner
as the very first entry in theINSTALLED_APPS
settingINSTALLED_APPS = [ 'spanner_django', ... ]
- Edit the
DATABASES
setting to point to an EXISTING database
DATABASES = {
'default': {
'ENGINE': 'spanner_django',
'PROJECT': '<project_id>',
'INSTANCE': '<instance_id>',
'NAME': '<database_name>',
# Only include this if you need to specify where to retrieve the
# service account JSON for the credentials to connect to Cloud Spanner.
'OPTIONS': {
'credentials_uri': '<credentials_uri>',
},
},
}
For example:
DATABASES = {
'default': {
'ENGINE': 'spanner_django',
'PROJECT': 'appdev-soda-spanner-staging', # Or the GCP project-id
'INSTANCE': 'django-dev1', # Or the Cloud Spanner instance
'NAME': 'db1', # Or the Cloud Spanner database to use
}
}
python-spanner-django
always works in autocommit
mode, which is Django's default behavior even for backends that support manual transaction management. Transactions cannot be controlled manually with calls like django.db.transaction.atomic()
.
Spanner doesn't have support for auto-generating primary key values. Therefore, python-spanner-django
monkey-patches AutoField
to generate a random UUID4. It generates a default using Field
's default
option which means AutoField
s will have a value when a model instance is created. For example:
>>> ExampleModel()
>>> ExampleModel.pk
4229421414948291880
To avoid hotspotting, these IDs are not monotonically increasing. This means that sorting models by ID isn't guaranteed to return them in the order in which they were created.
Spanner doesn't support ON DELETE CASCADE
when creating foreign-key constraints so python-spanner-django
doesn't support foreign key constraints.
Spanner doesn't support CHECK
constraints so one isn't created for PositiveIntegerField and CheckConstraint can't be used.
Spanner doesn't support a NUMERIC data type that allows storing high precision decimal values without the possibility of data loss.
Spanner doesn't support these functions.
This feature uses a column name that starts with an underscore (_order
) which Spanner doesn't allow.
Spanner doesn't support it. For example:
>>> ExampleModel.objects.order_by('?')
...
django.db.utils.ProgrammingError: 400 Function not found: RANDOM ... FROM
example_model ORDER BY RANDOM() ASC
Spanner has some limitations on schema changes which you must respect:
- Renaming tables and columns isn't supported.
- A column's type can't be changed.
- A table's primary key can't be altered.
- Migrations aren't atomic since
python-spanner-django
doesn't support transactions.
DurationField
arithmetic doesn't work with DateField
values (#253)
Spanner requires using different functions for arithmetic depending on the column type:
TIMESTAMP
columns (DateTimeField
) requireTIMESTAMP_ADD
orTIMESTAMP_SUB
DATE
columns (DateField
) requireDATE_ADD
orDATE_SUB
Django doesn't provide a way to determine which database function to use. DatabaseOperations.combine_duration_expression()
arbitrary uses TIMESTAMP_ADD
and TIMESTAMP_SUB
. Therefore, if you use a DateField
in a DurationField
expression, you'll see an error like: "No matching signature for function TIMESTAMP_ADD for argument types: DATE, INTERVAL INT64 DATE_TIME_PART."
Spanner doesn't support this.
For example, if integer
is IntegerField
:
>>> ExampleModel.objects.update(integer=F('integer') / 2)
...
django.db.utils.ProgrammingError: 400 Value of type FLOAT64 cannot be
assigned to integer, which has type INT64 [at 1:46]\nUPDATE
example_model SET integer = (example_model.integer /...
For example:
>>> Book.objects.annotate(adjusted_rating=F('rating') + None)
...
google.api_core.exceptions.InvalidArgument: 400 Operands of + cannot be literal
NULL ...