openwisp/openwisp-notifications

Notifications module of OpenWISP

openwisp-notifications's Issues

[bug] Make delete_obsolete_notifications resilient to failures

This happened while testing on openwisp-monitoring.

[2020-07-31 03:58:02,003: ERROR/ForkPoolWorker-5] Task openwisp_notifications.tasks.delete_obsolete_notifications[6a347c48-b253-4f77-bf73-430a48810e0a] raised unexpected: DoesNotExist('ContentType matching query does not exist.')
Traceback (most recent call last):
  File "/home/nemesis/.virtualenvs/openwisp2/lib/python3.7/site-packages/django/contrib/contenttypes/models.py", line 19, in get_by_natural_key
    ct = self._cache[self.db][(app_label, model)]
KeyError: 'default'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/nemesis/.virtualenvs/openwisp2/lib/python3.7/site-packages/celery/app/trace.py", line 412, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/home/nemesis/.virtualenvs/openwisp2/lib/python3.7/site-packages/celery/app/trace.py", line 704, in __protected_call__
    return self.run(*args, **kwargs)
  File "/home/nemesis/Code/openwisp/openwisp-notifications/openwisp_notifications/tasks.py", line 15, in delete_obsolete_notifications
    instance_app_label, instance_model
  File "/home/nemesis/.virtualenvs/openwisp2/lib/python3.7/site-packages/django/contrib/contenttypes/models.py", line 21, in get_by_natural_key
    ct = self.get(app_label=app_label, model=model)
  File "/home/nemesis/.virtualenvs/openwisp2/lib/python3.7/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/nemesis/.virtualenvs/openwisp2/lib/python3.7/site-packages/django/db/models/query.py", line 417, in get
    self.model._meta.object_name
django.contrib.contenttypes.models.ContentType.DoesNotExist: ContentType matching query does not exist.

Ensure the exception is catched and return from the task silently in these cases (it will happen when content types are removed from the DB).

[api/websocket] Skip notifications with missing data when iterating on notification list

Follow up to #44 (comment)

• raise an exception (a custom one we create for this purpose)
• catching this exception in the API and websocket when iterating on the notification list
• in case the exception is catched, the rendering of the notification is just skipped.

[JS] jQuery loaded twice

Two issues:

• these lines are not calling static like the other lines, why? https://github.com/openwisp/openwisp-notifications/blob/dev/openwisp_notifications/templates/admin/base_site.html#L29-L30
• jquery and jquery.init are loaded twice in pages where django already loads it on its own

I tried the following in base_site.html which seems to solve the issue, please double check and improve the solution if needed:

{% extends "admin/base_site.html" %}
{% load i18n static notification_tags %}

{% block extrastyle %}
  {{ block.super }}
  <link rel="stylesheet" type="text/css" href="{% static 'openwisp_notifications/css/loader.css' %}" />
  <link rel="stylesheet" type="text/css" href="{% static 'openwisp_notifications/css/notifications.css' %}" />
{% endblock extrastyle %}

{% block extrahead %}
{{ block.super }}
{% if 'jquery.js' not in media.js %}
<script type="text/javascript" src="{% static 'admin/js/vendor/jquery/jquery.js' %}"></script>
<script type="text/javascript" src="{% static 'admin/js/jquery.init.js' %}"></script>
{% endif %}
{% endblock %}

{% block userlinks %}
  <div class="ow-notifications" id="openwisp_notifications">
    <img class="bell-icon" src="{% static 'openwisp_notifications/images/icons/icon-bell.svg' %}" />
    {% unread_notifications %}
  </div>
  {% csrf_token %}
  {% notification_widget %}
{% endblock %}

{% block footer %}
  {{ block.super }}
  <script type="text/javascript">
    {% if OPENWISP_NOTIFICATIONS_HOST %}
      const notificationApiHost = new URL('{{ OPENWISP_NOTIFICATIONS_HOST }}');
    {% else %}
      const notificationApiHost = window.location;
    {% endif %}
    const notificationSound = new Audio('{{ OPENWISP_NOTIFICATIONS_SOUND }}');
  </script>

  <script type="text/javascript" src="{% static 'openwisp_notifications/js/vendor/reconnecting-websocket.min.js' %}"></script>
  <script type="text/javascript" src="{% static 'openwisp_notifications/js/notifications.js' %}"></script>
{% endblock footer %}

Please add a testcase for this bug which fails without the fix

[tests] django.db.utils.OperationalError: database table is locked: openwisp_notifications_notification

Happens randomly in tests (it can be seen sometimes on travis as well).

Using class based `notify_handler`

Instead of using a function, notify_handler can be implemented as a class which will provide ability to customise it without being the need to rewrite it completely. We can break it into small static methods to perform different aspects of generating a notification, like figuring out recipients, creating notification objects, etc. __call__ method can be used to make the class callable. This will make it extendable/customizable.

[admin] Ensure API URL used to get notifications is configurable

By default ajax requests will be sent to /, we need to make sure this is configurable, so we may be able to point out another domain.

[websockets] Delivering notifications at real-time

Notifications should be received and displayed on admin dashboard without reloading the page. A message(toast) should also be to notify upon receiving a new notification.

[qa] Improving manual testing

Currently, we are relying upon openwisp-monitoring for manually testing new features which are added to this module. We can ease this part by adding a model to the sample app.

Idea
Add a dummy model with name and organisation fields in the sample app. Register a notification type for this model.
A notification should be generated when objects of this model are created or deleted using this notification type. Notification should be received only by users of the same organisation.

Thanks to @NoumbissiValere for bringing this up, 👍

[tests] Switch test runner to openwisp_utils.tests.TimeLoggingTestRunner

Switch test runner to openwisp_utils.tests.TimeLoggingTestRunner.

[enhancement] Use IndxedDB for optimizing notification widget

Current implementation:

When a user opens any admin webpage. an API call to server is made through AJAX and notifications are fetched.
When user scrolls through the notification widget, more notifications are fetched from the server.
The notifications are stored on runtime memory of the browser to prevent subsequent calls to server.
Notification is marked read by sending a message through web sockets.

Shortcomings

• We need to keep track of read and unread notifications in the memory
• If a notification is created/deleted the notification widget is refreshed(reloaded) from the server.
• If user visits different pages on the admin site, API call are made to fetch same data each time.

Proposed Solution

• Use IndexedDB to cache notification data locally.
• When a user visits admin webpage for first time, API call is made to the server. Those notifications instead of getting stored in memory will be stored in IndexedDB.
• When user receives a new notification(through websocket) it will be updated in the IndexedDB and the notification will be updated.
• This will persist data over different webpages visited on admin site by user

Too many queries

@pandafy have you enabled the debug toolbar?
See here: http://openwisp.io/docs/developer/hacking-openwisp-python-django.html#django-debug-toolbar

Have you noticed the amount of queries?
Before we were storing the message but now we're generating it each time which generates far too many queries, so we should find a solution to this using caching (and we should handle cache invalidation).

one possible way of doing is the following :

• cache the actor object and try to retrieve it from the cache before querying
• same for target

Once the problem is fixed, we should add assertNumQueries in tests to make sure the amount of queries is kept under control.

I will arrange this in the board so it has less priority over the API and the JS widget.

[feature] Add notification types

Goals:

• Create a model NotificationType to categorize notifications.
• Add a markdown formatted message template which should be rendered as HTML to users on admin dashboard and mail.

Project Idea

Add the concept of notification type, it may be a list with some default values which can then be extended by each module.
Each notification type shall have a message which is generated from a configurable text template, the text shall be markdown formatted, the markdown text shall be expanded into HTML when the notification is sent via email or viewed via the JS widget.

Discussion
Project idea says to have some kind of list, in my opinion having a model will be more appropriate for this use case. .

[bug] You cannot use AsyncToSync in the same thread as an async event loop

This is appearing in a VM running openwisp-notifications dev branch.

raised unexpected: RuntimeError('You cannot use AsyncToSync in the same thread as an async event loop - just await the async function directly.')
Traceback (most recent call last):
  File "/opt/openwisp2/env/lib/python3.8/site-packages/celery/app/trace.py", line 412, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/opt/openwisp2/env/lib/python3.8/site-packages/celery/app/trace.py", line 704, in __protected_call__
    return self.run(*args, **kwargs)
  File "/opt/openwisp2/env/lib/python3.8/site-packages/openwisp_notifications/tasks.py", line 27, in delete_obsolete_notifications
    Notification.objects.filter(where).delete()
  File "/opt/openwisp2/env/lib/python3.8/site-packages/django/db/models/query.py", line 722, in delete
    deleted, _rows_count = collector.delete()
  File "/opt/openwisp2/env/lib/python3.8/site-packages/django/db/models/deletion.py", line 337, in delete
    signals.post_delete.send(
  File "/opt/openwisp2/env/lib/python3.8/site-packages/django/dispatch/dispatcher.py", line 173, in send
    return [
  File "/opt/openwisp2/env/lib/python3.8/site-packages/django/dispatch/dispatcher.py", line 174, in <listcomp>
    (receiver, receiver(signal=self, sender=sender, **named))
  File "/opt/openwisp2/env/lib/python3.8/site-packages/openwisp_notifications/handlers.py", line 172, in clear_notification_cache
    ws_handlers.notification_update_handler(
  File "/opt/openwisp2/env/lib/python3.8/site-packages/openwisp_notifications/websockets/handlers.py", line 13, in notification_update_handler
    async_to_sync(channel_layer.group_send)(
  File "/opt/openwisp2/env/lib/python3.8/site-packages/asgiref/sync.py", line 76, in __call__
    raise RuntimeError(
RuntimeError: You cannot use AsyncToSync in the same thread as an async event loop - just await the async function directly.

[docs] Document creating notifications in sample app

In #46 , dummy model was added to test whether notifications are being created and deleted.
Add documentation for this.

[feature] Allow users to ignore notifications on a specific object

• Allow a user to ignore notifications for a specific object, permanently or temporarily (1 day, 3 days, 1 week, 1 month, custom duration)
• Use celery to enable disabled notifications after passage of the specified time
• Provide an API to activate this feature of an object (eg: PUT /api/v1/notification/ignore/<content-type>/<object-id>/)
• Provide an API to deactivate this feature for an object (eg: DELETE /api/v1/notification/ignore/<content-type>/<object-id>/)

Project Idea

Allow users to disable notifications for specific objects, either permanently or until a specific date, with predefined set of durations: permanently, 1 day, 3 days, 1 week, 1 month, custom date. In the case the disabling is temporary, the setting should be deleted automatically after expiration by a simple celery task which is run periodically with celery beat.

[docs] Add feature list and screenshots to README

Add feature list and screenshots.

This should be done in the last phase of the project, or it can be done gradually (each time you add a feature you list it and document it, the screenshots can be added as last).

[feature] Notification settings: allow users to disable notifications by type, organization, medium

Goals

• Allow user to disable notifications by notification type.
• Allow possibility to disable only email notifications or web notifications.
• Allow disabling notification for an organization.

Project Idea

Allow users to disable notifications by notification types, right now it's only possible to enable or disable the notifications globally.
For each notification type and organization the user should be able to disable either all notifications or only the email notification.
Example: Receive notifications for organization "default"?
Two checkboxes: Web and Email; if email is checked also web is checked automatically (because the notification depends on the basic notification being created).
Such a solution would give us the possibility to implement mobile push notifications in the future by adding a new checkbox for mobile notifications.

Allow users to disable notifications for specific objects, either permanently or until a specific date, with predefined set of durations: permanently, 1 day, 3 days, 1 week, 1 month, custom date. In the case the disabling is temporary, the setting should be deleted automatically after expiration by a simple celery task which is run periodically with celery beat.

[chores] Fix hardcoded URLs in test_api

@pandafy always use reverse when generating URLs, I see there are some occurrences of hardcoded urls in test_api.py, if there are other occurrences fix those as well please.

[enhancement] Add `type_name` key to notification type

Currently, register_notification_type functions requires type_name to be provided separately.

Add type_name key in notification type configuration and use it instead of requiring an argument while registering notification type.

[feature] Develop API endpoints for listing notifications.

Goals

• Develop an API endpoint for listing notifications.
• Develop an API endpoint for marking notifications as read.

Project Idea

Create a javscript widget for the admin which allows to view all notification and expand their details by clicking on it.
This widget shall support infinite scrolling (we have a nice implementation in django-ipam which can be reused, either partially or totally) and expand the markdown into HTML.
The operation of opening a notification detail shall flag it as read.
This feature will require adding API endpoints to get notification list and details.

[models] Swappable models

• Implement Swappable Models
• Create a sample app to test swappable models
• Provide documentation about how to extend and customize this module

Useful resources:

• openwisp/openwisp-firmware-upgrader#60 (you can replicate what has been done here)

Edited by @pandafy

[bug] notifications JS widget fails in admin login page

How to replicate:

• log out from the admin, you'll be redirected to the login page
• watch the errors in the JS console

Expected result:

• no errors in the JS console

Actual result:

reconnecting-websocket.min.js:3 WebSocket connection to 'ws://localhost:8000/ws/notifications/' failed: Error during WebSocket handshake: Unexpected response code: 403
open @ reconnecting-websocket.min.js:3
a @ reconnecting-websocket.min.js:3
(anonymous) @ notifications.js:4
jquery.js:4046 jQuery.Deferred exception: Cannot read property 'scrollHeight' of undefined TypeError: Cannot read property 'scrollHeight' of undefined
    at onUpdate (http://localhost:8000/static/openwisp_notifications/js/notifications.js:124:58)
    at initNotificationWidget (http://localhost:8000/static/openwisp_notifications/js/notifications.js:165:9)
    at notificationWidget (http://localhost:8000/static/openwisp_notifications/js/notifications.js:177:5)
    at HTMLDocument.<anonymous> (http://localhost:8000/static/openwisp_notifications/js/notifications.js:14:9)
    at mightThrow (http://localhost:8000/static/admin/js/vendor/jquery/jquery.js:3762:29)
    at process (http://localhost:8000/static/admin/js/vendor/jquery/jquery.js:3830:12) undefinednnection to 'ws://localhost:8000/ws/notifications/' failed: Error during WebSocket handshake: Unexpected response code: 403
open @ reconnecting-websocket.min.js:3
(anonymous) @ reconnecting-websocket.min.js:3

Notification being sent to all users

If no organization and no recipient is provided in notify.send()then notifications will be sent to all users who have opted-in to receive notifications (notificationuser__receive=True).

openwisp-notifications/openwisp_notifications/handlers.py

Lines 32 to 51 in d2b2dd8

	where = Q()
	if target_org:
	where = Q(is_staff=True) & Q(openwisp_users_organization=target_org)
	where = where & Q(notificationuser__receive=True)
	if recipient:
	# Check if recipient is User, Group or QuerySet
	if isinstance(recipient, Group):
	recipients = recipient.user_set.filter(where)
	elif isinstance(recipient, (QuerySet, list)):
	recipients = recipient
	else:
	recipients = [recipient]
	else:
	where = where | (Q(is_superuser=True) & Q(notificationuser__receive=True))
	recipients = (
	User.objects.select_related('notificationuser')
	.order_by('date_joined')
	.filter(where)
	)

The problem arises at this statement

where = where | (Q(is_superuser=True) & Q(notificationuser__receive=True))

which update where as

(OR: ('notificationuser__receive', True), (AND: ('is_superuser', True), ('notificationuser__receive', True)))

A straight forward solution will be something like this

    where = Q()
    if target_org:
        where = Q(is_staff=True) & Q(openwisp_users_organization=target_org) & Q(notificationuser__receive=True)

    if recipient:
        # Check if recipient is User, Group or QuerySet
        if isinstance(recipient, Group):
            recipients = recipient.user_set.filter(notificationuser__receive=True)
        elif isinstance(recipient, (QuerySet, list)):
            recipients = recipient
        else:
            recipients = [recipient]
    else:
        where = where | (Q(is_superuser=True) & Q(notificationuser__receive=True))
        recipients = (
            User.objects.select_related('notificationuser')
            .order_by('date_joined')
            .filter(where)
        )

While this works, I have doubts that follows best practices since notificationuser__receive=True is redundant in this case. I would like to know your thoughts before proceeding.

This bug got introduced in #7

[docs] Incorrect syntax

I was referring to #19 for openwisp-monitoring/#86. Nice work in this PR 👏

I noticed a minor typo here so opened this issue 😄

...models.Site` ---> ...models.Site``

CC: @pandafy

[general] Create notifications in the background

As the amount of notifications generated by openwisp and the related rules about who to send to will grow, this will slow down the existing operations.

Every time an operation that can potentially generate a notification is executed (eg: when the notify signal is used), the calculations have to be performed and then acted upon, which may slow down execution when a large number of users are involved.

I think we should modify the notify signal to pass all the operations to a celery worker so the notification calculation and sending can happen entirely in the background.

This should not be hard, we have all the pieces of the puzzle in place, tests will execute celery tasks with EAGER set to True so it won't make a difference.

In settings.py we'd need the following as we have in monitoring and fw-upgrader:

if not TESTING:
    CELERY_BROKER_URL = 'redis://localhost/1'
else:
    CELERY_TASK_ALWAYS_EAGER = True
    CELERY_TASK_EAGER_PROPAGATES = True
    CELERY_BROKER_URL = 'memory://'

@pandafy can you investigate this please?

Keep in mind that when invoking a celery task, we shouldn't pass objects to it but only strings, integers, floats, because the values are serialized and passed from one process to another one.

[docs] Add animated gif to README

Add an animated gif to the readme which shows the notification widget in openwisp-monitoring.

This should be done right before the eng of GSoC, but wait for my greenlight to proceed please.

[bug] Strange interaction with firmware-upgrader

I have launched a firmware upgrade operation on an instance where I upgraded to the latest dev versions of openwisp-monitoring and openwisp-notifications and I started noticing notifications which we have not introduced yet, eg:

Giving up, device not reachable anymore after upgrade

timed out

I wonder WTF is happening?

Provided that this is a feature we do want to introduce, but as far as I know by the last time I reviewed the code, we were not doing this explicitly, so I think something wrong is going on here and it should be fixed.

@pandafy do you have any idea?

@NoumbissiValere @Vivekrajput20 FYI ☝️

[feature] Add a configurable email template

• A configurable email notification template.
• Configurable logo and CSS

Project Idea
Prepare a general email notification template which is configurable (can be changed with a setting) and defaults to using the default logo of OpenWISP (available in openwisp_utils.admin_theme). Make the logo configurable and add a way to supply extra CSS if needed.

[enhancement] Make defining base_site.html optional

Presently for a derivative app, we need to define admin/base_site.html so that it can work properly.
The main reason for this is presence of app label openwisp_notifications in url tag.

A way to solve this will be to override ModelAdmin and pass app label as a variable.

[ui] Fix notification number background when having > 99 notifications

When having a lot of notifications, the background of the notification count doesn't display correctly.

[docs] README

Copy structure of README from another module and adapt it to this module.

We'll be adding more info to the README as we go along.

[github] Remove GitHub action.

Remove the GitHub action for managing issues on Project board after GSoC 2020.

[chores] Remove support for "url" parameter in notify signal

In our use case with openwisp-monitoring, the url parameter is only passed for device. Since we are already building target_url for target object in openwisp-notifications, therefore url parameter can be removed to keep things simple.

[celery] Delete old notifications.

Goals

• Setup celery to deal with periodic class.
• Delete notifications older than a predefined time.

Project Idea

Add celery beat task to automatically delete notifications older than X days, X defaulting to 90, configurable via setting

[admin] Add a JS widget to browse notifications

• The widget should support infinite scrolling.
• User should be able to read description of notifications.
• Opening a notification should mark them as read

Project Idea

Create a javscript widget for the admin which allows to view all notification and expand their details by clicking on it.
This widget shall support infinite scrolling (we have a nice implementation in django-ipam which can be reused, either partially or totally) and expand the markdown into HTML.
The operation of opening a notification detail shall flag it as read.
This feature will require adding API endpoints to get notification list and details.

Should be done after #3

[email] Mark notification as read when user opens link to related object from email.

Instead of providing link to notification, provide link to related object. On opening this link, this notification should be automatically marked as read.

[docs] Update README

Update setup instructions in README.
Explicitly mention ordering of INSTALLED_APPS.

[tests] Add test for OPENWISP_NOTIFICATION_HTML_EMAIL=False

Use override_settings or mock.patch to set OPENWISP_NOTIFICATION_HTML_EMAIL to False in one test and write a test that ensures this feature works as expected.

[chores] static dir not consistent with other ow modules

Change static sub dir from openwisp_notifications/ to openwisp-notifications/ for consistency with other ow modules.

Release 0.1.0

@pandafy I think that after the API is done (#48) we can issue the first release of the module and publish it to pypi.

This should push us to make everything prettier (eg: eliminate all "TODO" placeholders from the readme) and will help the rest of the OpenWISP community to take this effort more seriously.

Once #48 is merged, can you please prepare a summary of the most relevant features we added in the change log (see CHANGES.rst in the other modules) please? And set the version to 0.1.0 final. I'll then proceed to publish it on pypi and add you as a maintainer (create an account there if you don't have one yet).

Thanks in advance.

[admin] Problems loading static files

After merging #29.
The notification bell icon doesn't render properly:

I suggest trying on openwisp-monitoring with the latest master of openwisp-notifications.

[js widget] UX problems found during testing

Where are all the notifications?

the widget shows always 10 notifications, even if there are more, it doesn't seem to load new data

Flagging notifications as read

The current way we implemented reading notifications is showing its limits: notifications are marked as read as soon as the widget is opened, which doesn't give us a chance to distinguish between read and unread ones.

A possible step forward could be to flag them as read on hover. The alternative could be leave it as it was before, so that they're marked unread only if clicked, and is up to the user to click on "mark all as read" if they don't want to click over every one.

HTTPs in dev

Clicking on a notification sends me to HTTPS also in dev mode.

@pandafy what do you think?

[bug] Notifications would be sent to staff users who are not organization managers

By double checking the code here: https://github.com/openwisp/openwisp-notifications/blob/dev/openwisp_notifications/handlers.py#L52, I think there is a bug in the following scenario:

• a staff user is organization manager of organization A
• the same user is also end user of organization B, but not manager

When notifications are generated for org B without specifying recipients, the user will get notifications even though they shouldn't.

The solution is to add OrganizationUser.is_admin=True to the where clause.

This issue has lower priority.

[setup] Pin down requirements

Please pin down the requirements being used:

https://github.com/openwisp/openwisp-notifications/blob/master/requirements.txt

Also, for the django-rest-framework dependency, do it like we're doing here:

• https://github.com/openwisp/openwisp-firmware-upgrader/pull/46/files#diff-354f30a63fb0907d4ad57269548329e3R40
• https://github.com/openwisp/openwisp-firmware-upgrader/pull/46/files#diff-2eeaed663bd0d25b7e608891384b7298R38

[email] Notification email not responsive

Opening email notifications with long subjects on mobile breaks HTML.

[bug] Mixed Content: ws loaded over HTTPs

Mixed Content: The page at 'https://URL/admin/config/' was loaded over HTTPS, but attempted to connect to the insecure WebSocket endpoint 'ws://URL/ws/notifications/'. This request has been blocked; this endpoint must be available over WSS.

Do not hardcode ws://.... The entire base url should be configurable, not just the host, and we have to make sure defaults to wss if settings.DEBUG is False.

[email] Truncated notification email subject

The subject of the email is truncated to 24 characters.

[ux] Problems found while testing toast notifications

Toasts are really great and very useful, they will allow us to do great things and inform the user in real time about what is going on in the network.

But we need to make the current implementation more robust.

• Have one style for each level (handled in 07200ac, PR #92)
• Keep the toast open longer (eg: 15 seconds?) so users won't miss them
• Add a close icon button to close it
• Mark as read on click or on close
• Allow having multiple toast notifications stacked, right now if I create two notifications, the last one cover the previous one, but as our usage of this tool increases, I am 100% sure in a busy system it's very likely two or more notifications can appear in a short time span when launching important changes to the network and we have to handle this well

[bug] 'NoneType' object has no attribute 'name'

I deleted some metrics, then went to the notifications page and this exception was raised:

AttributeError: 'NoneType' object has no attribute 'name'

We need to make this code more resilient to failures:
https://github.com/openwisp/openwisp-notifications/blob/master/openwisp_notifications/base/models.py#L54-L59

Any item may be missing for some reason.

Try to replicate it by generating notifications related to a metric in openwisp-monitoring and then delete the metric, try deleting any of the generic relations

A few things need to be done:

• write tests for this bug, one test for each generic relation that can be missing
• avoid the operation to fail so drastically, make sure something is shown anyway but log warnings in case the data is not as expected

Suggestions:

• try to avoid accessing attribute names in the notification message string if possible, ideally data should be passed as a variable
• wrap the operation in a try except block and if there's an exception, log a warning and provide a default value

Full stack trace:

KeyError: 'display_list_message'
  File "django/db/models/options.py", line 581, in get_field
    return self.fields_map[field_name]
FieldDoesNotExist: Notification has no field named 'display_list_message'
  File "django/contrib/admin/utils.py", line 262, in lookup_field
    f = _get_non_gfk_field(opts, name)
  File "django/contrib/admin/utils.py", line 293, in _get_non_gfk_field
    field = opts.get_field(name)
  File "django/db/models/options.py", line 583, in get_field
    raise FieldDoesNotExist("%s has no field named '%s'" % (self.object_name, field_name))
AttributeError: 'NoneType' object has no attribute 'name'
  File "django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "django/core/handlers/base.py", line 145, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "django/core/handlers/base.py", line 143, in _get_response
    response = response.render()
  File "django/template/response.py", line 105, in render
    self.content = self.rendered_content
  File "django/template/response.py", line 83, in rendered_content
    return template.render(context, self._request)
  File "django/template/backends/django.py", line 61, in render
    return self.template.render(context)
  File "django/template/base.py", line 171, in render
    return self._render(context)
  File "django/template/base.py", line 163, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "django/template/base.py", line 163, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "django/template/base.py", line 163, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "django/template/base.py", line 163, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "django/template/loader_tags.py", line 62, in render
    result = block.nodelist.render(context)
  File "django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "django/template/loader_tags.py", line 62, in render
    result = block.nodelist.render(context)
  File "django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "django/contrib/admin/templatetags/base.py", line 33, in render
    return super().render(context)
  File "django/template/library.py", line 214, in render
    _dict = self.func(*resolved_args, **resolved_kwargs)
  File "django/contrib/admin/templatetags/admin_list.py", line 342, in result_list
    'results': list(results(cl)),
  File "django/contrib/admin/templatetags/admin_list.py", line 318, in results
    yield ResultList(None, items_for_result(cl, res, None))
  File "django/contrib/admin/templatetags/admin_list.py", line 309, in __init__
    super().__init__(*items)
  File "django/contrib/admin/templatetags/admin_list.py", line 232, in items_for_result
    f, attr, value = lookup_field(field_name, result, cl.model_admin)
  File "django/contrib/admin/utils.py", line 271, in lookup_field
    value = attr(obj)
  File "openwisp_notifications/admin.py", line 116, in display_list_message
    return strip_tags(obj.message)
  File "django/utils/functional.py", line 48, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "openwisp_notifications/base/models.py", line 55, in message
    md_text = config['message'].format(notification=self)

[refractor] Make related object links cached_property

We are generating links to related objects at multiple places.

1. At admin dashboard.
2. While rendering markdown message
3. While fetching details of notifications using API.

We can instead create a property for these links and use them at other places.