django-model-versioning 0.1.1

A library to version a specific model, with references to specific and/or last version of it

Django Model Versioning

This library is used to create a model that get automatically versioned when specific fields are updated. When creating a relationship to such amodel you can choose if you want to create a standard relationship, that will connect your record to that specific version of the model, or create a relationship that will always point to the most updated version of the versioned entity instead.

Usage

1. First create the model you'd like to version like you'd normally do.

# myproject/taxes/models.py
from django.db.models import Model, CharField, DateTimeField, DecimalField


class Tax(Model):
    name = CharField(max_length=255, blank=False, null=False)
    percentage_value = DecimalField(max_digits=10, decimal_places=2, default=0)

    created_at = DateTimeField(auto_now_add=True)
    updated_at = DateTimeField(auto_now=True)

2. Then within your app create a versioning.py file

from lib.register import register
from lib.versioning_options import VersioningOptions
from taxes.models import Tax


@register(Tax)
class TaxVersioningOptions(VersioningOptions):
    versioned_fields = ('percentage_value',)

• We user @register(Tax) to tell django that these versioning options refer to the Tax model.
• The name of the class is unimportant, but it has to inherit from VersioningOptions
• Then we create the versioned_fields property and we specify which fields from the Tax model (or whatever model you register these options for) should be versioned. Whenever a versioned_field gets updated, a new version of the model is created and all references get updated.

3. Now we create a model that refers to that specific instance. We can just use a standard ForeignKey since the nehaviour we need here is the stadard one for Django references

from django.db.models import Model, IntegerField, DO_NOTHING, DateTimeField, ForeignKey

from taxes.models import Tax


class Payment(Model):
    amount = IntegerField()

    tax = ForeignKey(Tax, on_delete=DO_NOTHING)

    created_at = DateTimeField(auto_now_add=True)
    updated_at = DateTimeField(auto_now=True)

So in this case, each Payment we created will always refer to the same version of Tax 4. Now we create another model. This time we ant our new model to always refer to the last version of Tax

from django.db.models import Model, CharField, IntegerField, DateTimeField, DO_NOTHING

from lib.versioned_foreign_key import VersionedForeignKey
from taxes.models import Tax


class Product(Model):
    name = CharField(max_length=255, null=False, blank=False)
    price = IntegerField(null=False, default=0)

    tax = VersionedForeignKey(Tax, on_delete=DO_NOTHING)

    created_at = DateTimeField(auto_now_add=True)
    updated_at = DateTimeField(auto_now=True)

As we can see in the example, this time we don't use a ForeignField but rather a VersionedForeignField