django-related is a set of class-based-view mixins that help with common
scenarios that involves related objects. The generic class-based views like
``CreateView`` or ``UpdateView`` only deal with single objects. However, for
nested resources, or in cases where we might want to use an existing object if
avaialble, these views lack functionality. This is what django-related
Installation can be done using pip::
pip install django-related
There is no need to add ``related`` to installed apps. It can be used
from related.views import GetExistingMixin, CreateWithRelatedMixin
from related.views import GetExistingMixin
from django.views.gneric import CreateView
from models import Foo
class MyView(GetExistingMixin, CreateView):
model = Foo
existing_redirect_url = '/bar'
With the above view, if we submit a form that contains a ``pk`` or ``slug``
field, and the ``Foo`` object with matching ``pk`` or ``slug`` field exists,
user will be redirected to ``/bar`` path, and the model form for ``Foo`` will
not even be processed.
The view can be further customized using the following properties (and matching
Uses the specified form to process the request rather than request
parameters. Default is ``None`` (does no use forms).
Form field that contains data about existence of the object. Note that this
field does not need to evaluate to an actual object. Any non-``False``
value will be treated as signifying object's existence. The most common use
case is to use a ``ModelChoiceField`` or some field that reads the database
in advance, and provides a choice of values that are only available when
Dictionary of initial values for the ``existing_form_class`` form (if form
The model field that contains the primary key. Default is ``'pk'``.
The model field that contains the slug. Default is ``'slug'``
The request parameter that represents the primary key. Defalt is ``'pk'``.
The request parameter that represents the slug. Note that if primary key is
specified (it is by default), and it is passed in request, slug will not be
Required attribute. The URL that client will be redirected to if the object
Customizes the name of the context object containing the form.
This mixin is used when we are dealing with a ``CreateView`` for a nested
resource. The main assumption is that higher levels of the path contains a slug
or pk that points to the related model's object.
The key difference between normal CreateView, which can be persuaded to give
you the related object using the ``queryset`` attribute and ``get_object``
method, and this mixin, lies in the form processing. This mixin does two things
1. It ensures that the related object exists (behavior similar to
``get_object`` is forced)
2. It attaches the related object to the appropriate field in the submitted
Here is an example::
from related import CreateWithRelatedMixin
from django.views import CreateView
from models import Attachment, Post
from forms import CustomAttachmentModelForm
# View for `/posts/(?P<slug>[\w-]+)/attachments`
class AttachmentCreateView(CreateWithRelatedMixin, CreateView):
model = Attachment
form_class = CustomAttachmentModelForm
related_model = Post
With the above setup, the ``django.http.Http404`` is raised if GET request is
made to this view with the slug in the URL that points to a non-existent post.
If POST request is made to the same URL, ``django.http.HttpResponseGone`` (410)
is returned if post does not exist. Otherwise, the ``CustomAttachmentModelForm``
is processed, and the ``Post`` object that was found based on the slug will be
added to ``post`` field of the object resulting from the form processing.
The view can be customized using the following attributes (and matching
Related model under which the current model is nested. This attribute is
Field on the current model that must point to the related object. By
default, ``related_model``'s meta ``verbose_name`` is used.
If specified, the view will redirect instead of raising
``django.http.Http404`` or returning ``django.http.HttpResponseGone``.
Default is ``None``.
If ``related_404_redirect_url`` is used, the ``django.contrib.messages`` is
used to display an error message. This attribute is used to customize this
message. Default is ``'%s does not exist'`` where ``'%s'`` will evaluate to
the ``related_model``'s verbose name.
The field on the ``related_model`` that contains the primary key. Defaults
The URL parameter that contains the primary key. Defaults to ``'pk'``.
The field on the ``related_model`` that contains the sulug field. Defaults
The URL parameter that contains the slug field. Defaults to ``'slug'``.
Customizes name of the context object that contains the related object.
If there is an integrity error saving the object pointing to the related
object, the view will rerender the form, but will also add an error message
to the response object using ``django.contrib.messages``. This attribute
customizes the message. Default is ``'Such record already exists'``.
Please report bugs and feature requests to the Bitbucket `issue tracker`_.
.. _issue tracker: https://bitbucket.org/monwara/django-related/issues