adamhaney/django-ondelta

A django model mixin that makes it easy to react to field value changes on models. Supports an API similar to the model clean method.

django-ondelta

A django model mixin that makes it easy to react to field value changes on models. Supports an API similar to the model clean method.

Quick Start

Given that I have the model

class MyModel(models.Model):
    mai_field = models.CharField()
    other_field = models.BooleanField()

And I want to be notified when mai_field's value is changed and persisted I would simply need to modify my model to include a ondelta_mai_field method.

from ondelta.models import OnDeltaMixin

class MyModel(OnDeltaMixin):
    mai_field = models.CharField()
    other_field = models.BooleanField()

    def ondelta_mai_field(self, old_value, new_value):
        print("mai field had the value of {}".format(old_value))
        print("but after we called save it had the value of {}".format(new_value))

This is the easiest method to watch a single field for changes, but what if we want to perform an action that has an aggregate view of all of the fields that were changed? OnDeltaMixin provides an ondelta_all method for these cases; it is only called once for each save.

from ondelta.models import OnDeltaMixin

class MyModel(OnDeltaMixin):
    mai_field = models.CharField()
    other_field = models.BooleanField()

    ondelta_all(self, fields_changed):
        if 'mai_field' in fields_changed and 'other_field' in fields_changed:
            print("Both fields changed during this save!")

Unsupported Field Types

Some field types are not supported: ManyToManyField, reverse ManyToManyField, reverse ForeignKey, and reverse OneToOneField relations. If you create an ondelta_field_name method for one of these fields, it will not be called when that field is changed.

Help

I like to help people as much as possible who are using my libraries, the easiest way to get my attention is to tweet @adamhaney or open an issue. As long as I'm able I'll help with any issues you have.

django-ondelta's Issues

License?

What is the license for django-ondelta? I see the LICENSE file says MIT, but in setup.py, it says LGPL.

ondelta_[Field] is giving incorrect value for _state.adding

ondelta_[Field] is giving incorrect value for _state.adding

def clean(self):
    print(self._state.adding) # Output: True
    ...

def ondelta_name(self, old_value, new_value):
    print(self._state.adding) # Output: False
    ...

Expected Output: True

Django 1.9 Support

A change in Django 1.9, officially released today, has caused importing OnDeltaMixin to fail. Just wanted to leave an example stack trace here while I work on a possible solution.

File "/var/www/bellhops/kinetic/hophr/models.py", line 11, in <module>
    from ondelta.models import OnDeltaMixin
  File "/home/vagrant/.venv/lib/python3.4/site-packages/ondelta/models.py", line 12, in <module>
    class OnDeltaMixin(models.Model):
  File "/home/vagrant/.venv/lib/python3.4/site-packages/django/db/models/base.py", line 94, in __new__
    app_config = apps.get_containing_app_config(module)
  File "/home/vagrant/.venv/lib/python3.4/site-packages/django/apps/registry.py", line 239, in get_containing_app_config
    self.check_apps_ready()
  File "/home/vagrant/.venv/lib/python3.4/site-packages/django/apps/registry.py", line 124, in check_apps_ready
    raise AppRegistryNotReady("Apps aren't loaded yet.")

TypeError: add() argument after * must be a sequence, not RelatedManager

Here are the models:

class Foo(OnDeltaModel):
    name = models.CharField(max_length=50)
    is_public = models.BooleanField(default=False)

class Bar(models.Model):
    foo = models.ForeignKey(models.Model, related_name='items'):

And the traceback:

>>> foo.save()
Traceback (most recent call last):
  File "[...]python2.7/site-packages/IPython/core/interactiveshell.py", line 2827, in run_code
    exec code_obj in self.user_global_ns, self.user_ns
  File "<ipython-input-10-6970514bfc33>", line 1, in <module>
    c.save()
  File "[...]python2.7/site-packages/ondelta/models.py", line 75, in save
    self._ondelta_dispatch_notifications()
  File "[...]python2.7/site-packages/ondelta/models.py", line 55, in _ondelta_dispatch_notifications
    setattr(self._ondelta_shadow, field, changes['new'])
  File "[...]python2.7/site-packages/django/db/models/fields/related.py", line 404, in __set__
    manager.add(*value)
TypeError: add() argument after * must be a sequence, not RelatedManager

It happens because 'items' returns as a field name in the _ondelta_fields_to_watch() method of Foo, although it's not a field. django.db.models.options.get_all_field_names() includes reverse relation names.