Django Model Mixin for field change monitoring

has_changed_model_mixin.py

from __future__ import unicode_literals

from django.db import models

# Create your models here.

class HasChangedModelMixin(models.Model):
    class Meta:
        abstract = True

    @classmethod
    def from_db(cls, db, field_names, values):
        # https://docs.djangoproject.com/en/1.10/ref/models/instances/#customizing-model-loading
        instance = super(HasChangedModelMixin, cls).from_db(db, field_names, values)
        # customization to store the original field values on the instance
        instance._loaded_values = dict(zip(field_names, values))
        return instance

    def has_field_changed(self, field_name):
        if self._state.adding:
            return False

        return getattr(self, field_name) != self._loaded_values[field_name]