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A mixin that allows models to register methods that are notified when their values change,or register a method that is notified of all changes. Basically, OnDeltaMixin implementsthe observer pattern.

Project description

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.

Project details


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