Django Hashid Field

A custom Model Field that uses the Hashids library to obfuscate an IntegerField or AutoField. It can be used in new models or dropped in place of an existing IntegerField, explicit AutoField, or an automatically generated AutoField.

Features

• Stores IDs as integers in the database
• Allows lookups and filtering by hashid string or Hashid object and (optionally) integer.
• Can enable integer lookups globally or per-field
• Can be used as sort key
• Can drop-in replace an existing IntegerField (HashidField) or AutoField (HashidAutoField)
• Allows specifying a salt globally
• Supports custom salt, min_length, alphabet and allow_int_lookup settings per field
• Supports Django REST Framework Serializers
• Supports common filtering lookups, such as field__icontains so that Django Admin search_fields works out of the box.
• Supports subquery lookups with field__in=queryset
• Supports hashing operations so the fields can be used in Dictionaries and Sets.

Requirements

This module is tested and known to work with:

• Python 2.7, 3.5
• Django 1.8, 1.9, 1.10, 1.11
• Hashids 1.2
• Django REST Framework 3.6

Installation

Install the package (preferably in a virtualenv):

$ pip install django-hashid-field

Configure a global SALT for all HashidFields to use by default in your settings.py.

HASHID_FIELD_SALT = "a long and secure salt value that is not the same as SECRET_KEY"
# Note: You can generate a secure key with:
#     from django.core.management.utils import get_random_secret_key; print(get_random_secret_key())

Add it to your model

from hashid_field import HashidField

class Book(models.Model):
    reference_id = HashidField()

Migrate your database

$ ./manage.py makemigrations
$ ./manage.py migrate

Upgrading

Potentially breaking changes in 2.0.0 depending on your usage and configuration, specifically if you rely on integer lookups (now off by default) or exceptions for invalid lookup values.

Please see the Change Log

Basic Usage

Use your field like you would any other, for the most part. You can assign integers:

>>> b = Book()
>>> b.reference_id = 123
>>> b.reference_id
Hashid(123): OwLxW8D

You can assign valid hashids. It's valid only if it can be decoded into an integer based on your settings:

>>> b.reference_id = 'r8636LO'
>>> b.reference_id
Hashid(456): r8636LO

You can access your field with either hashid strings or Hashid objects:

>>> Book.objects.filter(reference_id='OwLxW8D')
<QuerySet [<Book:  (OwLxW8D)>]>
>>> b = Book.objects.get(reference_id='OwLxW8D')
>>> b
<Book:  (OwLxW8D)>
>>> h = b.reference_id
>>> h
Hashid(123): OwLxW8D
>>> Book.objects.filter(reference_id=h)
<Book:  (OwLxW8D)>

You can lookup objects with integers if you set HASHID_FIELD_ALLOW_INT_LOOKUP = True or allow_int_lookup=True as a parameter to the field.

reference_id = HashidField(allow_int_lookup=True)

Now integer lookups are allowed. Useful if migrating an existing AutoField to a HashidAutoField, but you need to allow lookups with older integers.

>>> Book.objects.filter(reference_id=123)
<QuerySet [<Book:  (OwLxW8D)>]>

The objects returned from a HashidField are an instance of the class Hashid, and allow basic access to the original integer or the hashid:

>>> from hashid_field import Hashid
>>> h = Hashid(123)
>>> h.id
123
>>> h.hashid
'Mj3'
>>> print(h)
Mj3
>>> repr(h)
'Hashid(123): Mj3'

Hashid Auto Field

Along with HashidField there is also a HashidAutoField that works in the same way, but that auto-increments just like an AutoField.

from hashid_field import HashidAutoField

class Book(models.Model):
    serial_id = HashidAutoField(primary_key=True)

The only difference is that if you don't assign a value to it when you save, it will auto-generate a value from your database, just as an AutoField would do. Please note that HashidAutoField inherits from AutoField and there can only be one AutoField on a model at a time.

>>> b = Book()
>>> b.save()
>>> b.serial_id
Hashid(1): AJEM7LK

It can be dropped into an existing model that has an auto-created AutoField (all models do by default) as long as you give it the same name and set primary_key=True. So if you have this model:

class Author(models.Model):
    name = models.CharField(max_length=40)

Then Django has created a field for you called 'id' automatically. We just need to override that by specifying our own field with primary_key set to True.

class Author(models.Model):
    id = HashidAutoField(primary_key=True)
    name = models.CharField(max_length=40)

And now you can use the 'id' or 'pk' attributes on your model instances:

>>> a = Author.objects.create(name="John Doe")
>>> a.id
Hashid(60): N8VNa8z
>>> Author.objects.get(pk='N8VNa8z')
<Author: Author object>

Global Settings

HASHID_FIELD_SALT

You can optionally set a global Salt to be used by all HashFields and HashidAutoFields in your project. Do not use the same string as your SECRET_KEY, as this could lead to your SECRET_KEY being exposed to an attacker. Please note that changing this value will cause all HashidFields to change their values, and any previously published IDs will become invalid. Can be overridden by the field definition.

Type:	string
Default:	""
Example:	HASHID_FIELD_SALT = "a long and secure salt value that is not the same as SECRET_KEY"

HASHID_FIELD_ALLOW_INT_LOOKUP

Allow lookups or fetches of fields using the underlying integer that's stored in the database. Disabled by default to prevent users from being to do a sequential scan of objects by pulling objects by integers (1, 2, 3) instead of Hashid strings ("Ba9p1AG", "7V9gk9Z", "wro12zm"). Can be overriden by the field definition.

Type:	boolean
Default:	False
Example:	HASHID_FIELD_ALLOW_INT_LOOKUP = True

HASHID_FIELD_LOOKUP_EXCEPTION

By default any invalid hashid strings or integer lookups when integer lookups are turned off will result in an EmptyResultSet being returned. Enable this to instead throw a ValueError exception (similar to the behavior prior to 2.0).

Type:	boolean
Default:	False
Example:	HASHID_FIELD_LOOKUP_EXCEPTION = True

Field Parameters

Besides the standard field options, there are settings you can tweak that are specific to HashidField and AutoHashidField.

Please note that changing any of the values for salt, min_length or alphabet will affect the obfuscation of the integers that are stored in the database, and will change what are considered "valid" hashids. If you have links or URLs that include your HashidField values, then they will stop working after changing any of these values. It's highly advised that you don't change any of these settings once you publish any references to your field.

salt

Type:	string
Default:	settings.HASHID_FIELD_SALT, ""
Example:	reference_id = HashidField(salt="Some salt value")

min_length

Type:	int
Default:	7
Note:	This defaults to 7 for the field since the maximum IntegerField value can be encoded in 7 characters with the default alphabet setting of 62 characters.
Example:	reference_id = HashidField(min_length=15)

alphabet

Type:	string of characters (16 minimum)
Default:	Hashids.ALPHABET, which is "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"
Example:	# Only use numbers and lower-case letters reference_id = HashidField(alphabet="0123456789abcdefghijklmnopqrstuvwxyz")

allow_int_lookup

Type:	boolean
Default:	settings.HASHID_FIELD_ALLOW_INT_LOOKUP, False
Example:	reference_id = HashidField(allow_int_lookup=True)

Hashid Class

Operations with a HashidField or HashidAutoField return a Hashid object. This simple class does the heavy lifting of converting integers and hashid strings back and forth. There shouldn't be any need to instantiate these manually.

Methods

__init__(id, salt='', min_length=0, alphabet=Hashids.ALPHABET):

id:	REQUIRED Integer you wish to encode
salt:	Salt to use. Default: ''
min_length:	Minimum length of encoded hashid string. Default: 0
alphabet:	The characters to use in the encoded hashid string. Default: Hashids.ALPHABET

Read-Only Properties

id

type:	Int
value:	The decoded integer

hashid

type:	String
value:	The encoded hashid string

hashids

type:	Hashids()
value:	The instance of the Hashids class that is used to encode and decode

Django REST Framework Integration

If you wish to use a HashidField or HashidAutoField with a DRF ModelSerializer, there is one extra step that you must take. Automatic declaration of any Hashid*Fields will result in an ImproperlyConfigured exception being thrown. You must explicitly declare them in your Serializer, as there is no way for the generated field to know how to work with a Hashid*Field, specifically what 'salt', 'min_length' and 'alphabet' to use, and can lead to very difficult errors or behavior to debug, or in the worst case, corruption of your data. Here is an example:

from rest_framework import serializers
from hashid_field.rest import HashidSerializerCharField


class BookSerializer(serializers.ModelSerializer):
    reference_id = HashidSerializerCharField(source_field='library.Book.reference_id')

    class Meta:
        model = Book
        fields = ('id', 'reference_id')

The source_field allows the HashidSerializerCharField to copy the 'salt', 'min_length' and 'alphabet' settings from the given field at app_name.model_name.field_name so that it can be defined in just one place. Explicit settings are also possible:

reference_id = HashidSerializerCharField(salt="a different salt", min_length=10, alphabet="ABCDEFGHIJKLMNOPQRSTUVWXYZ")

If nothing is given, then the field will use the same global settings as a Hashid*Field. It is very important that the options for the serializer field matches the model field, or else strange errors or data corruption can occur.

HashidSerializerCharField will serialize the value into a Hashids string, but will deserialize either a Hashids string or integer and save it into the underlying Hashid*Field properly. There is also a HashidSerializerIntegerField that will serialize the Hashids into an un-encoded integer as well.

Primary Key Related Fields

Any models that have a ForeignKey to another model that uses a Hashid*Field as its Primary Key will need to explicitly define how the PrimaryKeyRelatedField should serialize and deserialize the resulting value using the pk_field argument. For the given Author model defined above that has an id = HashidAutoField(primary_key=True) set, your BookSerializer should look like the following.

from rest_framework import serializers
from hashid_field.rest import HashidSerializerCharField


class BookSerializer(serializers.ModelSerializer):
    author = serializers.PrimaryKeyRelatedField(pk_field=HashidSerializerCharField(source_field='library.Author.id'), read_only=True)

    class Meta:
        model = Book
        fields = ('id', 'author')

Make sure you pass the source field to the HashidSerializer*Field so that it can copy the 'salt', 'min_length' and 'alphabet' as described above.

This example sets read_only=True but you can explicitly define a queryset or override get_queryset(self) to allow read-write behavior.

For a ManyToManyField, you must also remember to pass many=True to the PrimaryKeyRelatedField.

HashidSerializerCharField

Serialize a Hashid*Field to a Hashids string, de-serialize either a valid Hashids string or integer into a Hashid*Field.

Parameters

source_field

A 3-field dotted notation of the source field to load matching 'salt', 'min_length' and 'alphabet' settings from. Must be in the format of "app_name.model_name.field_name". Example: "library.Book.reference_id".

salt, min_length, alphabet

See Field Parameters

HashidSerializerIntegerField

Serialize a Hashid*Field to an integer, de-serialize either a valid Hashids string or integer into a Hashid*Field. See HashidSerializerCharField for parameters.

Development

Here are some rough instructions on how to set up a dev environment to develop this module. Modify as needed. The sandbox is a django project that uses django-hashid-id, and is useful for developing features with.

• git clone https://github.com/nshafer/django-hashid-field.git && cd django-hashid-field
• mkvirtualenv -a . -p /usr/bin/python3 -r sandbox/requirements.txt django-hashid-field
• python setup.py develop
• sandbox/manage.py migrate
• sandbox/manage.py createsuperuser
• sandbox/manage.py loaddata authors books editors
• sandbox/manage.py runserver
• python runtests.py

For any pull requests, clone the repo and push to it, then create the PR.

To install the latest development version, use:

` pip install git+https://github.com/nshafer/django-hashid-field.git `

LICENSE

MIT License. You may use this in commercial and non-commercial projects with proper attribution. Please see the LICENSE