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Class-based-views mixins for handling related objects

Project description

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 provides.


Installation can be done using pip:

pip install django-related

There is no need to add related to installed apps. It can be used directly:

from related.views import GetExistingMixin, CreateWithRelatedMixin


Basic usage:

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 methods):

existing_form_class (get_existing_form_class())

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 objects exist.

existing_form_initial (get_existing_form_initial())

Dictionary of initial values for the existing_form_class form (if form is used).


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 looked up.

existing_redirect_url (get_existing_redirect_url())

Required attribute. The URL that client will be redirected to if the object exists.

existing_form_name (get_existing_form_name)

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 differently:

  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 object.

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 methods):


Related model under which the current model is nested. This attribute is required.


Field on the current model that must point to the related object. By default, related_model’s meta verbose_name is used.

related_404_redirect_url (get_related_404_url())

If specified, the view will redirect instead of raising django.http.Http404 or returning django.http.HttpResponseGone. Default is None.

related_404_message (get_rlated_404_message)

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 to 'pk'.


The URL parameter that contains the primary key. Defaults to 'pk'.


The field on the related_model that contains the sulug field. Defaults to 'slug'.


The URL parameter that contains the slug field. Defaults to 'slug'.

related_object_name (get_related_object_name)

Customizes name of the context object that contains the related object.

integritiy_error_message (get_integrity_error_message())

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'.

cache_backend (get_cache_backend)

Specifies the object that implements the caching methods. This object is django.core.caching.cache by default. Any interface that you specify must provide the same methods as the default one.

Reporting bugs

Please report bugs and feature requests to the Bitbucket issue tracker.

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