Welcome to django-dirtyfields’s documentation!

Tracking dirty fields on a Django model instance. Dirty means that field in-memory and database values are different.

Source code

Install

$ pip install django-dirtyfields

Usage

To use django-dirtyfields, you need to:

• Inherit from DirtyFieldsMixin in the Django model you want to track.

from django.db import models
from dirtyfields import DirtyFieldsMixin

class TestModel(DirtyFieldsMixin, models.Model):
    """A simple test model to test dirty fields mixin with"""
    boolean = models.BooleanField(default=True)
    characters = models.CharField(blank=True, max_length=80)

• Use one of these 2 functions on a model instance to know if this instance is dirty, and get the dirty fields:

  • is_dirty()
  • get_dirty_fields()

Examples

>>> from tests.models import TestModel
>>> tm = TestModel.objects.create(boolean=True,characters="testing")
>>> tm.is_dirty()
False
>>> tm.get_dirty_fields()
{}

>>> tm.boolean = False

>>> tm.is_dirty()
True
>>> tm.get_dirty_fields()
{'boolean': True}

Checking foreign key fields.

By default, dirty functions are not checking foreign keys. If you want to also take these relationships into account, use check_relationship parameter:

>>> from tests.models import TestModel
>>> tm = TestModel.objects.create(fkey=obj1)
>>> tm.is_dirty()
False
>>> tm.get_dirty_fields()
{}

>>> tm.fkey = obj2

>>> tm.is_dirty()
False
>>> tm.is_dirty(check_relationship=True)
True

>>> tm.get_dirty_fields()
{}
>>> tm.get_dirty_fields(check_relationship=True)
{'fkey': 1}

Checking many-to-many fields.

By default, dirty functions are not checking many-to-many fields. They are also a bit special, as a call to .add() method is directly saving the related object to the database, thus the instance is never dirty. If you want to check these relations, you should set ENABLE_M2M_CHECK to True in your model inheriting from DirtyFieldsMixin, use check_m2m parameter and provide the values you want to test against:

class TestM2MModel(DirtyFieldsMixin, models.Model):
    ENABLE_M2M_CHECK = True
    m2m_field = models.ManyToManyField(AnotherModel)

>>> from tests.models import TestM2MModel
>>> tm = TestM2MModel.objects.create()
>>> tm2 = TestModel.objects.create()
>>> tm.is_dirty()
False
>>> tm.m2m_field.add(tm2)
>>> tm.is_dirty()
False
>>> tm.get_dirty_fields(check_m2m={'m2m_field': set([tm2.id])})
{}
>>> tm.get_dirty_fields(check_m2m={'m2m_field': set(["dummy_value])})
{'m2m_field': set([tm2.id])}

This can be useful when validating forms with m2m relations, where you receive some ids and want to know if your object in the database needs to be updated with these form values.

WARNING: this m2m mode will generate extra queries to get m2m relation values each time you will save your objects. It can have serious performance issues depending on your project.

Checking a limited set of model fields.

If you want to check a limited set of model fields, you should set FIELDS_TO_CHECK in your model inheriting from DirtyFieldsMixin:

class TestModelWithSpecifiedFields(DirtyFieldsMixin, models.Model):
    boolean1 = models.BooleanField(default=True)
    boolean2 = models.BooleanField(default=True)
    FIELDS_TO_CHECK = ['boolean1']

>>> from tests.models import TestModelWithSpecifiedFields
>>> tm = TestModelWithSpecifiedFields.objects.create()

>>> tm.boolean1 = False
>>> tm.boolean2 = False

>>> tm.get_dirty_fields()
{'boolean1': True}

This can be used in order to increase performance.

Saving dirty fields.

If you want to only save dirty fields from an instance in the database (only these fields will be involved in SQL query), you can use save_dirty_fields method.

Warning: this save_dirty_fields method will trigger the same signals as django default save method. But, in django 1.4.22-, as we are using under the hood an update method, we need to manually send these signals, so be aware that only sender and instance arguments are passed to the signal in that context.

>>> tm.get_dirty_fields()
{'fkey': 1}
>>> tm.save_dirty_fields()
>>> tm.get_dirty_fields()
{}

Verbose mode

By default, when you use get_dirty_fields function, if there are dirty fields, only the old value is returned. You can use verbose option to have more informations, for now a dict with old and new value:

>>> tm.get_dirty_fields()
{'fkey': 1}
>>> tm.get_dirty_fields(verbose=True)
{'fkey': {'saved': 1, 'current': 3}}

Custom comparison function

By default, dirtyfields compare the value between the database and the memory on a naive way (==). After some issues (with timezones for example), a customisable comparison logic has been added. You can now define how you want to compare 2 values by passing a function on DirtyFieldsMixin:

from django.db import models
from dirtyfields import DirtyFieldsMixin

def your_function((new_value, old_value, param1):
    # Your custom comparison code here
    return new_value == old_value

class TestModel(DirtyFieldsMixin, models.Model):
    compare_function = (your_function, {'param1': 5})

Have a look at dirtyfields.compare module to get some examples.

Custom value normalisation function

By default, dirtyfields reports on the dirty fields as is. If a date field was changed the result of get_dirty_fields will return the current and saved datetime object. In some cases it is useful to normalise those values, e.g., when wanting ot save the diff data as a json dataset in a database. The default behaviour of using values as is can be changed by providing a normalise_function in your model. That function can evaluate the value’s type and rewrite it accordingly.

This example shows the usage of the normalise function, with an extra paramter of a user’s timezone being passed as well:

::

import pytz import datetime from django.db import models from dirtyfields import DirtyFieldsMixin

def your_normalise_function(value, timezone=None):

if isinstance(value, (datetime.datetime, datetime.date)):

if timezone:

return pytz.timezone(timezone).localize(value).isoformat()

else:

return value.isoformat()

else:

return value

def get_user_timezone():

return ‘Europe/London’

class TestModel(DirtyFieldsMixin, models.Model):

normalise_function = (your_normalise_function, {‘timezone’: get_user_timezone()})

Why would you want this?

When using django.db.models.signals (django.db.models.signals.pre_save especially), it is useful to be able to see what fields have changed or not. A signal could change its behaviour depending on whether a specific field has changed, whereas otherwise, you only could work on the event that the model’s save() method had been called.

Contributing

If you’re interested in developing it, you can launch project tests on that way:

$ pip install tox
$ pip install -e .
$ tox

Credits

This code has largely be adapted from what was made available at Stack Overflow.

Table of Contents:

• Contributing
• Credits

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