Save The Change

Save The Change takes this:

>>> lancelot = Knight.objects.get(name="Sir Lancelot")
>>> lancelot.favorite_color = "Blue"
>>> lancelot.save()

And does this:

UPDATE "roundtable_knight"
SET "favorite_color" = 'Blue'

Instead of this:

UPDATE "roundtable_knight"
SET "name" = 'Sir Lancelot',
    "from" = 'Camelot',
    "quest" = 'To seek the Holy Grail.',
    "favorite_color" = 'Blue',
    "epithet" = 'The brave',
    "actor" = 'John Cleese',
    "full_name" = 'John Marwood Cleese',
    "height" = '6''11"',
    "birth_date" = '1939-10-27',
    "birth_union" = 'UK',
    "birth_country" = 'England',
    "birth_county" = 'Somerset',
    "birth_town" = 'Weston-Super-Mare',
    "facial_hair" = 'mustache',
    "graduated" = true,
    "university" = 'Cambridge University',
    "degree" = 'LL.B.',

Installation

Install Save The Change just like everything else:

$ pip install django-save-the-change

Usage

Just add the SaveTheChange decorator to your model:

from django.db import models
from save_the_change.decorators import SaveTheChange

@SaveTheChange
class Knight(models.model):
        ...

And that’s it! Keep using Django like you always have, Save The Change will take care of you.

How It Works

Save The Change encapsulates the fields of your model with its own descriptors that track their values for any changes. When you call save(), Save The Change passes the names of your changed fields through Django’s update_fields argument, and Django does the rest, sending only those fields back to the database.

Caveats

Save The Change can’t help you with ManyToManyFields nor reverse relations, as those aren’t handled through save(). But everything else should work.

Goodies

Save The Change also comes with two additional decorators, TrackChanges and UpdateTogether.

TrackChanges provides some additional properties and methods to keep interact with changes made to your model, including comparing the old and new values and reverting any changes to your model before you save it. It can be used independently of SaveTheChange.

UpdateTogether is an additional decorator which allows you to specify groups of fields that are dependent on each other in your model, ensuring that if any of them change they’ll all be saved together. For example:

from django.db import models
from save_the_change.decorators import SaveTheChange, UpdateTogether

@SaveTheChange
@UpdateTogether(('height_feet', 'height_inches'))
class Knight(models.model):
        ...

Now if you ever make a change to either part of our Knight’s height, both the feet and the inches will be sent to the database together, so that they can’t accidentally fall out of sync.