Skip to main content

Extends django check constraint to support annotations.

Project description

django-check-constraint

django check constraint test. PyPI version PyPI - License PyPI - Python Version PyPI - Django Version Upload Python Package Create New Release

Extends Django's Check constraint with support for UDF(User defined functions/db functions) and annotations.

Installation

$ pip install django-check-constraint

ADD check_constraint to list of INSTALLED APPS.

INSTALLED_APPS = [
  ...
  "check_constraint",
  ...
]

Scenario:

Suppose you have a database function that returns the counts of null values in [i, ...n].

CREATE OR REPLACE FUNCTION public.non_null_count(VARIADIC arg_array ANYARRAY)
  RETURNS BIGINT AS
  $$
    SELECT COUNT(x) FROM UNNEST($1) AS x
  $$ LANGUAGE SQL IMMUTABLE;

Example:

SELECT public.non_null_count(1, null, null);

Outputs:

non_null_count
----------------
              1
(1 row)

Defining a check constraint with this function

The equivalent of (PostgresSQL)

ALTER TABLE app_name_test_modoel ADD CONSTRAINT app_name_test_model_optional_field_provided
    CHECK(non_null_count(amount::integer , amount_off::integer, percentage::integer) = 1);

Usage

Converting this to django functions and annotated check contraints can be done using:

function.py

from django.db.models import Func, SmallIntegerField, TextField
from django.db.models.functions import Cast


class NotNullCount(Func):
    function = 'non_null_count'

    def __init__(self, *expressions, **extra):
        filter_exp = [
            Cast(exp, TextField()) for exp in expressions if isinstance(exp, str)
        ]
        if 'output_field' not in extra:
            extra['output_field'] = SmallIntegerField()

        if len(expressions) < 2:
            raise ValueError('NotNullCount must take at least two expressions')

        super().__init__(*filter_exp, **extra)

Creating annotated check constraints

from django.db import models
from django.db.models import Q
from check_constraint.models import AnnotatedCheckConstraint

class TestModel(models.Model):
    amount = models.DecimalField(max_digits=9, decimal_places=2, null=True, blank=True)
    amount_off = models.DecimalField(max_digits=7, decimal_places=2, null=True, blank=True)
    percentage = models.DecimalField(max_digits=3, decimal_places=0, null=True, blank=True)


    class Meta:
        constraints = [
            AnnotatedCheckConstraint(
                check=Q(not_null_count=1),
                annotations={
                    'not_null_count': (
                        NotNullCount(
                            'amount',
                            'amount_off',
                            'percentage',
                        )
                    ),
                },
                name='%(app_label)s_%(class)s_optional_field_provided',
            ),
        ]

TODO's

  • [ ] Add support for schema based functions.
  • [ ] Add warning about mysql lack of user defined check constraint support.
  • [ ] Remove skipped sqlite3 test.

Project details


Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Files for django-check-constraint, version 1.0.18
Filename, size File type Python version Upload date Hashes
Filename, size django_check_constraint-1.0.18-py3-none-any.whl (14.5 kB) File type Wheel Python version py3 Upload date Hashes View
Filename, size django-check-constraint-1.0.18.tar.gz (13.6 kB) File type Source Python version None Upload date Hashes View

Supported by

Pingdom Pingdom Monitoring Google Google Object Storage and Download Analytics Sentry Sentry Error logging AWS AWS Cloud computing DataDog DataDog Monitoring Fastly Fastly CDN DigiCert DigiCert EV certificate StatusPage StatusPage Status page