# Field Extensions

synopsis:

  Field Extensions

Database model field extensions.

## AutoSlugField

AutoSlugField will automatically create a unique slug incrementing an appended number on the slug until it is unique. Inspired by SmileyChris’ Unique Slugify snippet.

AutoSlugField takes a populate_from argument that specifies which field, list of fields, or model method the slug will be populated from, for instance:

    slug = AutoSlugField(populate_from=['title', 'description', 'get_author_name'])

populate_from can traverse a ForeignKey relationship by using Django ORM syntax:

    slug = AutoSlugField(populate_from=['related_model__title', 'related_model__get_readable_name'])

AutoSlugField uses Django’s slugify function by default to “slugify” `populate_from` field.

To provide custom “slugify” function you could either provide the function as an argument to `AutoSlugField` or define your `slugify_function` method within a model.

1. `slugify_function` as an argument to `AutoSlugField`.

>     # models.py

>     from django.db import models

>     from django_extensions.db.fields import AutoSlugField

>     def my_slugify_function(content):
>         return content.replace('_', '-').lower()

>     class MyModel(models.Model):

>         title = models.CharField(max_length=42)
>         slug = AutoSlugField(populate_from='title', slugify_function=my_slugify_function)

2. `slugify_function` as a method within a model class.

>     # models.py

>     from django.db import models

>     from django_extensions.db.fields import AutoSlugField

>     class MyModel(models.Model):

>         title = models.CharField(max_length=42)
>         slug = AutoSlugField(populate_from='title')

>         def slugify_function(self, content):
>             return content.replace('_', '-').lower()

> Important. If you both provide `slugify_function` in a model class and pass `slugify_function` to `AutoSlugField` field, then model’s `slugify_function` method will take precedence.

## RandomCharField

AutoRandomCharField will automatically create a unique random character field with the specified length. By default upper/lower case and digits are included as possible characters. Given a length of 8 that yields 3.4 million possible combinations. A 12 character field would yield about 2 billion. Below are some examples:

    >>> RandomCharField(length=8, unique=True)
    BVm9GEaE

    >>> RandomCharField(length=4, include_alpha=False)
    7097

    >>> RandomCharField(length=12, include_punctuation=True)
    k[ZS.TR,0LHO

    >>> RandomCharField(length=12, lowercase=True, include_digits=False)
    pzolbemetmok

## CreationDateTimeField

A `DateTimeField` that will automatically set its date when the object is first saved to the database. Works in the same way as the auto_now_add keyword.

## ModificationDateTimeField

A `DateTimeField` that will automatically set its date when an object is saved to the database. Works in the same way as the auto_now keyword. It is possible to preserve the current timestamp by setting update_modified to False:

    >>> example = MyTimeStampedModel.objects.get(pk=1)

    >>> print example.modified
    datetime.datetime(2016, 3, 18, 10, 3, 39, 740349, tzinfo=<UTC>)

    >>> example.save(update_modified=False)

    >>> print example.modified
    datetime.datetime(2016, 3, 18, 10, 3, 39, 740349, tzinfo=<UTC>)

    >>> example.save()

    >>> print example.modified
    datetime.datetime(2016, 4, 8, 14, 25, 43, 123456, tzinfo=<UTC>)

It is also possible to set the attribute directly on the model, for example when you don’t use the TimeStampedModel provided in this package, or when you are in a migration:

    >>> example = MyCustomModel.objects.get(pk=1)

    >>> print example.modified
    datetime.datetime(2016, 3, 18, 10, 3, 39, 740349, tzinfo=<UTC>)

    >>> example.update_modified=False

    >>> example.save()

    >>> print example.modified
    datetime.datetime(2016, 3, 18, 10, 3, 39, 740349, tzinfo=<UTC>)

## ShortUUIDField

A `CharField` which transparently generates a UUID and pass it to base57. It result in shorter 22 characters values useful e.g. for concise, unambiguous URLS. It’s possible to get shorter values with length parameter: they are not Universal Unique any more but probability of collision is still low.

## JSONField

A generic `TextField` that neatly serializes/unserializes JSON objects seamlessly. Django 1.9 introduces a native JSONField for PostgreSQL, which is preferred for PostgreSQL users on Django 1.9 and above.