rsinger86/django-lifecycle

Declarative model lifecycle hooks, an alternative to Signals.

django
django-models
lifecycle-hooks
transition-conditions

Django Lifecycle Hooks

Package version Python versions Python versions PyPI - Django Version

This project provides a @hook decorator as well as a base model and mixin to add lifecycle hooks to your Django models. Django's built-in approach to offering lifecycle hooks is Signals. However, my team often finds that Signals introduce unnecessary indirection and are at odds with Django's "fat models" approach.

Django Lifecycle Hooks supports:

  • Python 3.7, 3.8, 3.9, 3.10, 3.11, and 3.12
  • Django 2.2, 3.2, 4.0, 4.1, 4.2, and 5.0

In short, you can write model code like this:

from django_lifecycle import LifecycleModel, hook, BEFORE_UPDATE, AFTER_UPDATE


class Article(LifecycleModel):
    contents = models.TextField()
    updated_at = models.DateTimeField(null=True)
    status = models.ChoiceField(choices=['draft', 'published'])
    editor = models.ForeignKey(AuthUser)

    @hook(BEFORE_UPDATE, WhenFieldHasChanged("contents", has_changed=True))
    def on_content_change(self):
        self.updated_at = timezone.now()

    @hook(
        AFTER_UPDATE, 
        condition=(
            WhenFieldValueWas("status", value="draft")
            & WhenFieldValueIs("status", value="published")
        )
    )
    def on_publish(self):
        send_email(self.editor.email, "An article has published!")

Instead of overriding save and __init__ in a clunky way that hurts readability:

    # same class and field declarations as above ...

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self._orig_contents = self.contents
        self._orig_status = self.status


    def save(self, *args, **kwargs):
        if self.pk is not None and self.contents != self._orig_contents:
            self.updated_at = timezone.now()

        super().save(*args, **kwargs)

        if self.status != self._orig_status:
            send_email(self.editor.email, "An article has published!")

Documentation: https://rsinger86.github.io/django-lifecycle

Source Code: https://github.com/rsinger86/django-lifecycle


Changelog

See Changelog

Testing

Tests are found in a simplified Django project in the /tests folder. Install the project requirements and do ./manage.py test to run them.

License

See License.

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