Django Lifecycle Hooks

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 3.5, 3.6, 3.7, 3.8 and 3.9, Django 2.0.x, 2.1.x, 2.2.x, 3.0.x and 3.1.x.

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, when='contents', has_changed=True)
    def on_content_change(self):
        self.updated_at = timezone.now()

    @hook(AFTER_UPDATE, when="status", was="draft", is_now="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!")

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

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

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Changelog

0.9.1 (March 2021)

• Makes hooks work with OneToOneFields. Thanks @bahmdev!

0.9.0 (February 2021)

• Prevents calling a hooked method twice with the same state. Thanks @garyd203!

0.8.1 (January 2021)

• Added missing return to delete() method override. Thanks @oaosman84!

0.8.0 (October 2020)

• Significant performance improvements. Thanks @dralley!

0.7.7 (August 2020)

• Fixes issue with GenericForeignKey. Thanks @bmbouter!

0.7.6 (May 2020)

• Updates to use constants for hook names; updates docs to indicate Python 3.8/Django 3.x support. Thanks @thejoeejoee!

0.7.5 (April 2020)

• Adds static typed variables for hook names; thanks @Faisal-Manzer!
• Fixes some typos in docs; thanks @tomdyson and @bmispelon!

0.7.1 (January 2020)

• Fixes bug in utils._get_field_names that could cause recursion bug in some cases.

0.7.0 (December 2019)

• Adds changes_to condition - thanks @samitnuk! Also some typo fixes in docs.

0.6.1 (November 2019)

• Remove variable type annotation for Python 3.5 compatability.

0.6.0 (October 2019)

• Adds when_any hook parameter to watch multiple fields for state changes

0.5.0 (September 2019)

• Adds was_not condition
• Allow watching changes to FK model field values, not just FK references

0.4.2 (July 2019)

• Fixes missing README.md issue that broke install.

0.4.1 (June 2019)

• Fixes urlman-compatability.

0.4.0 (May 2019)

• Fixes initial_value(field_name) behavior - should return value even if no change. Thanks @adamJLev!

0.3.2 (February 2019)

• Fixes bug preventing hooks from firing for custom PKs. Thanks @atugushev!

0.3.1 (August 2018)

• Fixes m2m field bug, in which accessing auto-generated reverse field in before_create causes exception b/c PK does not exist yet. Thanks @garyd203!

0.3.0 (April 2018)

• Resets model's comparison state for hook conditions after save called.

0.2.4 (April 2018)

• Fixed support for adding multiple @hook decorators to same method.

0.2.3 (April 2018)

• Removes residual mixin methods from earlier implementation.

0.2.2 (April 2018)

• Save method now accepts skip_hooks, an optional boolean keyword argument that controls whether hooked methods are called.

0.2.1 (April 2018)

• Fixed bug in _potentially_hooked_methods that caused unwanted side effects by accessing model instance methods decorated with @cache_property or @property.

0.2.0 (April 2018)

• Added Django 1.8 support. Thanks @jtiai!
• Tox testing added for Python 3.4, 3.5, 3.6 and Django 1.8, 1.11 and 2.0. Thanks @jtiai!

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.