django-hashid-field 2.0.0

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Django Hashid Field
====================

A custom Model Field that uses the `Hashids <http://hashids.org/>`_ `library <https://pypi.python.org/pypi/hashids/>`_
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):

.. code-block:: bash

$ pip install django-hashid-field

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

.. code-block:: python

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

.. code-block:: python

from hashid_field import HashidField

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

Migrate your database

.. code-block:: bash

$ ./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 <https://github.com/nshafer/django-hashid-field/blob/master/CHANGELOG.md>`_

Basic Usage
-----------

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

.. code-block:: python

>>> 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:

.. code-block:: python

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

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

.. code-block:: python

>>> 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.

.. code-block:: python

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.

.. code-block:: python

>>> 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:

.. code-block:: python

>>> 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``.

.. code-block:: python

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.

.. code-block:: python

>>> 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:

.. code-block:: python

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.

.. code-block:: python

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:

.. code-block:: python

>>> 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:
.. code-block:: python

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:
.. code-block:: python

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:
.. code-block:: python

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:
.. code-block:: python

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:
.. code-block:: python

reference_id = HashidField(min_length=15)

alphabet
~~~~~~~~

:Type: string of characters (16 minimum)
:Default: Hashids.ALPHABET, which is "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"
:Example:
.. code-block:: python

# 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:
.. code-block:: python

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:

.. code-block:: python

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:

.. code-block:: python

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 <http://www.django-rest-framework.org/api-guide/relations/#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.

.. code-block:: python

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 <https://github.com/nshafer/django-hashid-field/blob/master/LICENSE>`_