Pint Fields for Django and Postgres
Project description
django-pint-field
Use pint with Django's ORM.
If you want to store quantities (1 gram, 3 miles, 8.120391 angstroms, etc) in a model, edit them in forms, and have the ability to convert to other quantities in your django projects, this is the package for you!
This package is modified from the fantastic django-pint with different goals. Unlike django-pint, in this project we use a composite Postgres field to store both the magnitude and the user's desired units, along with the equivalent value in base units. This third piece of date - the base units - makes it possible to conduct lookups comparing one instance that might be specified in "grams" with another that may be specified in "pounds", but display each instance in the units that the user desires. The units your users want to use are the units they see, while still allowing accurate comparisons of one quantity to another.
For this reason, the project only works with Postgresql databases.
Install
pip install django_pint_field
Add "django_pint_field",
to your list of installed apps.
Run python manage.py migrate django_pint_field
Usage
Assuming we are starting with the following model:
from decimal import Decimal
from django.db import models
from django.db.models import DecimalField
from django_pint_field.models import IntegerPintField
class IntegerPintFieldSaveModel(models.Model):
name = models.CharField(max_length=20)
weight = IntegerPintField("gram")
def __str__(self):
return str(self.name)
We can do the following:
from decimal import Decimal
from django_pint_field.units import ureg
from .models import IntegerPintFieldSaveModel
Quantity = ureg.Quantity
# Start by creating a few Pint Quantity objects
extra_small = Quantity(1 * ureg.gram)
small = Quantity(10 * ureg.gram)
medium = Quantity(100 * ureg.gram)
large = Quantity(1000 * ureg.gram)
extra_large = Quantity(10000 * ureg.gram)
# Create a couple objects
IntegerPintFieldSaveModel.objects.create(name="small", weight=small)
IntegerPintFieldSaveModel.objects.create(name="large", weight=large)
In [1]: IntegerPintFieldSaveModel.objects.first()
Out[1]: <IntegerPintFieldSaveModel: small>
In [2]: IntegerPintFieldSaveModel.objects.first().weight
Out[2]: 10 <Unit('gram')>
In [3]: IntegerPintFieldSaveModel.objects.first().weight.magnitude
Out[3]: 10
In [4]: IntegerPintFieldSaveModel.objects.first().weight.units
Out[4]: <Unit('gram')>
Valid Lookups
Other lookups will be added in the future. Currently available are:
- exact
- gt
- gte
- lt
- lte
- range
- isnull
# Perform some queries
IntegerPintFieldSaveModel.objects.filter(weight__gt=medium)
<QuerySet [<IntegerPintFieldSaveModel: large>]>
IntegerPintFieldSaveModel.objects.filter(weight__gt=extra_small)
<QuerySet [<IntegerPintFieldSaveModel: small>, <IntegerPintFieldSaveModel: large>]>
IntegerPintFieldSaveModel.objects.filter(weight__gte=small)
<QuerySet [<IntegerPintFieldSaveModel: small>, <IntegerPintFieldSaveModel: large>]>
IntegerPintFieldSaveModel.objects.filter(weight__range=(small, medium))
<QuerySet [<IntegerPintFieldSaveModel: small>]>
Aggregates
A number of aggregates have been implemented for the Django Pint Fields. Functionally they perform for Pint Fields the same way django's default aggregates work for other field types, and each is prepended with "Pint". The aggregates include:
- PintAvg
- PintCount
- PintMax
- PintMin
- PintStdDev
- PintSum
- PintVariance
from django_pint_field.aggregates import PintAvg, PintCount, PintMax, PintMin, PintStdDev, PintSum, PintVariance
# Perform some queries
IntegerPintFieldSaveModel.objects.aggregate(PintAvg('weight'))
{'weight__pintavg': Decimal('0.50500000000000000000') <Unit('kilogram')>}
IntegerPintFieldSaveModel.objects.aggregate(PintCount('weight'))
{'weight__pintcount': 2}
IntegerPintFieldSaveModel.objects.aggregate(PintMax('weight'))
{'weight__pintmax': Decimal('1.0') <Unit('kilogram')>}
IntegerPintFieldSaveModel.objects.aggregate(PintMin('weight'))
{'weight__pintmin': Decimal('0.01') <Unit('kilogram')>}
IntegerPintFieldSaveModel.objects.aggregate(PintStdDev('weight'))
{'weight__pintstddev': Decimal('0.49500000000000000000') <Unit('kilogram')>}
IntegerPintFieldSaveModel.objects.aggregate(PintSum('weight'))
{'weight__pintsum': Decimal('1.01') <Unit('kilogram')>}
IntegerPintFieldSaveModel.objects.aggregate(PintVariance('weight'))
{'weight__pintvariance': Decimal('0.24502500000000000000') <Unit('kilogram')>}
Use with Django Rest Framework
from django_pint_field.rest import IntegerPintRestField
class DjangoPintFieldSerializer(serializers.ModelSerializer):
# Let DRF know which type of serializer field to use
weight = IntegerPintRestField()
class Meta:
model = IntegerPintFieldSaveModel
fields = ["name", "weight"]
Creating your own units
You can create your own pint units if the default units in pint are not sufficient.
Anywhere within your project (ideally in settings or a file adjacent to settings), define the custom unit registry by importing Pint's default UnitRegistry and extending it:
from pint import UnitRegistry
custom_ureg = UnitRegistry()
custom_ureg.define("custom = [custom]")
custom_ureg.define("kilocustom = 1000 * custom")
Then add the custom registry to your app's settings.py:
DJANGO_PINT_FIELD_UNIT_REGISTER = custom_ureg
Model Fields
- IntegerPintField: Stores a pint measurement as an integer (-2147483648 to 2147483647).
- BigIntegerPintField: Stores a pint measurement as a big integer (-9223372036854775808 to 9223372036854775807).
- DecimalPintField: Stores a pint measurement as a decimal. Like Django's DecimalField, DecimalPintField takes required
max_digits
anddecimal_places
parameters.
Form Fields
- IntegerPintFormField: Used in forms with IntegerPintField and BigIntegerPintField.
- DecimalPintFormField: Used in forms with DecimalPintField.
Widgets
- PintFieldWidget: Default widget for all django pint field types.
DRF Serializer Fields
- IntegerPintRestField: Used in DRF with IntegerPintField and BigIntegerPintField.
- DecimalPintRestField: Used in DRF with DecimalPintField.
Settings
DJANGO_PINT_FIELD_DECIMAL_PRECISION
-
Determines whether django_pint_field should automatically set the python decimal precision for the project. If an integer greater than 0 is provided, the decimal context precision for the entire project will be set to that value. Otherwise, the precision remains at the default (usually 28).
* Type: int * Default: 0 DJANGO_PINT_FIELD_UNIT_REGISTER
-
The Unit Registry to use in the project. Defaults to pint.UnitRegistry.
* Type: int * Default: 0
Rounding modes (upcoming feature)
decimal.ROUND_CEILING Round towards Infinity.
decimal.ROUND_DOWN Round towards zero.
decimal.ROUND_FLOOR Round towards -Infinity.
decimal.ROUND_HALF_DOWN Round to nearest with ties going towards zero.
decimal.ROUND_HALF_EVEN Round to nearest with ties going to nearest even integer.
decimal.ROUND_HALF_UP Round to nearest with ties going away from zero.
decimal.ROUND_UP Round away from zero.
decimal.ROUND_05UP Round away from zero if last digit after rounding towards zero would have been 0 or 5; otherwise round towards zero.
Read more about rounding modes for decimals at the decimal docs
Use the test app with docker compose
Set up a virtual environment (recommended)
Make a virtual environment named .venv
:
python3 -m venv .venv
Activate the new environment:
source .venv/bin/activate
Install dependencies
Requires poetry. If you do not yet have it installed, run pip install poetry
.
poetry install --with dev
Build and bring up
docker compose build
docker compose run django python manage.py migrate
docker compose run django python manage.py createsuperuser
docker compose up -d
Navigate to 127.0.0.1:8000
Test (assuming you have already performed build
)
docker compose run django python manage.py test
Run psql on the Postgres database
docker compose exec postgres psql -U postgres
ToDos:
- Implement rounding modes
- Think through what it would take to build range types for these fields
- Add extensible widget template
Project details
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