Decorators for quickly setting up links to related model instances in the Django admin.

admin_decorators.py

"""
Sometimes it can be useful to quickly navigate between objects.
This module defines two useful decorators:

  * admin_link
  * admin_changelist_link

Borrowed, with love, from:
https://medium.com/@hakibenita/things-you-must-know-about-django-admin-as-your-app-gets-bigger-6be0b0ee9614
"""

from django.core.urlresolvers import reverse
from django.forms.forms import pretty_name
from django.utils.html import format_html
from functools import wraps, reduce


def getattr_nested(obj, attr):
    return reduce(getattr, [obj] + attr.split('__'))


def admin_change_url(obj):
    app_label = obj._meta.app_label
    model_name = obj._meta.model.__name__.lower()
    return reverse('admin:{}_{}_change'.format(
        app_label, model_name
    ), args=(obj.pk,))


def admin_link(attr, short_description=None, empty_description="-"):
    """Decorator used for rendering a link to a related model in
    the admin detail page.

    attr (str):
        Name of the related field.
    short_description (str):
        Name if the field.
    empty_description (str):
        Value to display if the related field is None.

    The wrapped method receives the related object and should
    return the link text.

    Usage:
        @admin_link('credit_card', _('Credit Card'))
        def credit_card_link(self, credit_card):
            return credit_card.name
    """
    def wrap(func):
        @wraps(func)
        def field_func(self, obj):
            related_obj = getattr_nested(obj, attr)
            if related_obj is None:
                return empty_description
            url = admin_change_url(related_obj)
            return format_html(
                '<a href="{}">{}</a>',
                url,
                func(self, related_obj)
            )
        field_func.short_description = short_description if short_description else pretty_name(attr)
        field_func.allow_tags = True
        return field_func
    return wrap


def admin_changelist_url(model):
    app_label = model._meta.app_label
    model_name = model.__name__.lower()
    return reverse('admin:{}_{}_changelist'.format(
        app_label,
        model_name)
    )


def admin_changelist_link(attr, short_description=None, empty_description="-", query_string=None):
    """Decorator used for rendering a link to the list display of
    a related model in the admin detail page.

    attr (str):
        Name of the related field.
    short_description (str):
        Field display name.
    empty_description (str):
        Value to display if the related field is None.
    query_string (function):
        Optional callback for adding a query string to the link.
        Receives the object and should return a query string.

    The wrapped method receives the related object and
    should return the link text.

    Usage:
        @admin_changelist_link('products', _('Products'), query_string=lambda c: 'category_id={}'.format(c.pk))
        def credit_card_link(self, credit_card):
            return credit_card.name
    """
    def wrap(func):
        @wraps(func)
        def field_func(self, obj):
            related_obj = getattr_nested(obj, attr)
            if related_obj is None:
                return empty_description
            url = admin_changelist_url(related_obj.model)
            if query_string:
                url += '?' + query_string(obj)
            return format_html(
                '<a href="{}">{}</a>',
                url,
                func(self, related_obj)
            )
        field_func.short_description = short_description if short_description else pretty_name(attr)
        field_func.allow_tags = True
        return field_func
    return wrap