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==============
django-related
==============

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
============

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
    ...


GetExistingMixin
================

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).

``existing_form_field``
    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).

``existing_pk_field``
    The model field that contains the primary key. Default is ``'pk'``.

``existing_slug_field``
    The model field that contains the slug. Default is ``'slug'``

``existing_request_pk_key``
    The request parameter that represents the primary key. Defalt is ``'pk'``.

``existing_request_slug_key``
    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.

CreateWithRelatedMixin
======================

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.

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 post with the
slug as in the URL 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``
    Related model under which the current model is nested. This attribute is
    required.

``related_field``
    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``. 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.
    
``related_pk_field``
    The field on the ``related_model`` that contains the primary key. Defaults
    to ``'pk'``.

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

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

``related_slug_url_kwarg``
    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'``.

Reporting bugs
==============

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

.. _issue tracker: https://bitbucket.org/monwara/django-related/issues