Field change aware Django Model

models.py

from django.db import models


class StoredOriginalValuesModel(models.Model):
    """
    Model that stores original data in a dictionary and provides the
    field_has_changed(field_name) method to check if a field has been modified
    after loading the data from the db.
    Original values are stored in the _original dictionary only when creating
    the object or calling refresh_from_db(), so the field_has_changed() method
    works even after save().
    """
    class Meta:
        abstract = True

    def __init__(self, *args, **kwargs):
        super(StoredOriginalValuesModel, self).__init__(*args, **kwargs)
        self.store_original_values()

    def refresh_from_db(self, *args, **kwargs):
        super(StoredOriginalValuesModel, self).refresh_from_db(*args, **kwargs)
        self.store_original_values()

    def store_original_values(self):
        """
        Store the current model data as original values.
        """
        all_fields = self._meta.get_fields(include_parents=True)
        # TODO: check how to store ForeingKeys and ManyToManys
        fields = [x for x in all_fields if not x.is_relation]
        self._original = {}
        for field in fields:
            self._original[field.name] = field.value_from_object(self)

    def field_has_changed(self, field):
        """
        Verifies if a field was changed since last refresh from db.
        """
        if field not in self._original:
            raise Exception('Field not found in stored original values: %s' % field)
        return self._original[field] != getattr(self, field)

    def changed_fields(self):
        """
        Returns a list of all changed fields.
        """
        changed_fields = []
        for field in self._original.keys():
            if self.field_has_changed(field):
                changed_fields.append(field)
        return changed_fields