Rework misc config to run exactly one query

There should never be that much stuff in MiscConfig, so let's just read
it all and deal with it in python instead of trying to run one query
for each item of interest and poorly cache it.

This PR also moved MiscConfigDict into a middleware so it can be used
outside of templates.

dmoj/settings.py

@@ -287,6 +287,7 @@ MIDDLEWARE = (
     'judge.middleware.APIMiddleware',
     'django.middleware.csrf.CsrfViewMiddleware',
     'django.contrib.auth.middleware.AuthenticationMiddleware',
+    'judge.middleware.MiscConfigMiddleware',
     'judge.middleware.DMOJLoginMiddleware',
     'django.contrib.messages.middleware.MessageMiddleware',
     'django.middleware.clickjacking.XFrameOptionsMiddleware',

judge/middleware.py

@@ -6,11 +6,15 @@ from urllib.parse import quote
 
 from django.conf import settings
 from django.contrib.auth.models import User
+from django.contrib.sites.shortcuts import get_current_site
+from django.core.cache import cache
 from django.http import HttpResponse, HttpResponseRedirect
 from django.urls import Resolver404, resolve, reverse
 from django.utils.encoding import force_bytes
 from requests.exceptions import HTTPError
 
+from judge.models import MiscConfig
+
 try:
     import uwsgi
 except ImportError:
@@ -130,3 +134,46 @@ class APIMiddleware(object):
             response.status_code = 401
             return response
         return self.get_response(request)
+
+
+class MiscConfigDict(dict):
+    __slots__ = ('language', 'site', 'backing')
+
+    def __init__(self, language='', domain=None):
+        self.language = language
+        self.site = domain
+        self.backing = None
+        super().__init__()
+
+    def __missing__(self, key):
+        if self.backing is None:
+            cache_key = 'misc_config'
+            backing = cache.get(cache_key)
+            if backing is None:
+                backing = dict(MiscConfig.objects.values_list('key', 'value'))
+                cache.set(cache_key, backing, 86400)
+            self.backing = backing
+
+        keys = ['%s.%s' % (key, self.language), key] if self.language else [key]
+        if self.site is not None:
+            keys = ['%s:%s' % (self.site, key) for key in keys] + keys
+
+        for attempt in keys:
+            result = self.backing.get(attempt)
+            if result is not None:
+                break
+        else:
+            result = ''
+
+        self[key] = result
+        return result
+
+
+class MiscConfigMiddleware:
+    def __init__(self, get_response):
+        self.get_response = get_response
+
+    def __call__(self, request):
+        domain = get_current_site(request).domain
+        request.misc_config = MiscConfigDict(language=request.LANGUAGE_CODE, domain=domain)
+        return self.get_response(request)

judge/signals.py

@@ -2,10 +2,9 @@ import errno
 import os
 
 from django.conf import settings
-from django.contrib.sites.models import Site
 from django.core.cache import cache
 from django.core.cache.utils import make_template_fragment_key
-from django.db.models.signals import post_delete, post_save, pre_save
+from django.db.models.signals import post_delete, post_save
 from django.dispatch import receiver
 
 from .caching import finished_submission
@@ -128,35 +127,14 @@ def organization_update(sender, instance, **kwargs):
                        for engine in EFFECTIVE_MATH_ENGINES])
 
 
-_misc_config_i18n = [code for code, _ in settings.LANGUAGES]
-_misc_config_i18n.append('')
-
-
-def misc_config_cache_delete(key):
-    cache.delete_many(['misc_config:%s:%s:%s' % (domain, lang, key.split('.')[0])
-                       for lang in _misc_config_i18n
-                       for domain in Site.objects.values_list('domain', flat=True)])
-
-
-@receiver(pre_save, sender=MiscConfig)
-def misc_config_pre_save(sender, instance, **kwargs):
-    try:
-        old_key = MiscConfig.objects.filter(id=instance.id).values_list('key').get()[0]
-    except MiscConfig.DoesNotExist:
-        old_key = None
-    instance._old_key = old_key
-
-
 @receiver(post_save, sender=MiscConfig)
 def misc_config_update(sender, instance, **kwargs):
-    misc_config_cache_delete(instance.key)
-    if instance._old_key is not None and instance._old_key != instance.key:
-        misc_config_cache_delete(instance._old_key)
+    cache.delete('misc_config')
 
 
 @receiver(post_delete, sender=MiscConfig)
 def misc_config_delete(sender, instance, **kwargs):
-    misc_config_cache_delete(instance.key)
+    cache.delete('misc_config')
 
 
 @receiver(post_save, sender=ContestSubmission)

judge/template_context.py

@@ -3,11 +3,10 @@ from functools import partial
 from django.conf import settings
 from django.contrib.auth.context_processors import PermWrapper
 from django.contrib.sites.shortcuts import get_current_site
-from django.core.cache import cache
 from django.utils.functional import SimpleLazyObject, new_method_proxy
 
 from judge.utils.caniuse import CanIUse, SUPPORT
-from .models import MiscConfig, NavigationBar, Profile
+from .models import NavigationBar, Profile
 
 
 class FixedSimpleLazyObject(SimpleLazyObject):
@@ -71,37 +70,8 @@ def site(request):
     return {'site': get_current_site(request)}
 
 
-class MiscConfigDict(dict):
-    __slots__ = ('language', 'site')
-
-    def __init__(self, language='', domain=None):
-        self.language = language
-        self.site = domain
-        super(MiscConfigDict, self).__init__()
-
-    def __missing__(self, key):
-        cache_key = 'misc_config:%s:%s:%s' % (self.site, self.language, key)
-        value = cache.get(cache_key)
-        if value is None:
-            keys = ['%s.%s' % (key, self.language), key] if self.language else [key]
-            if self.site is not None:
-                keys = ['%s:%s' % (self.site, key) for key in keys] + keys
-            map = dict(MiscConfig.objects.values_list('key', 'value').filter(key__in=keys))
-            for item in keys:
-                if item in map:
-                    value = map[item]
-                    break
-            else:
-                value = ''
-            cache.set(cache_key, value, 86400)
-        self[key] = value
-        return value
-
-
 def misc_config(request):
-    domain = get_current_site(request).domain
-    return {'misc_config': MiscConfigDict(domain=domain),
-            'i18n_config': MiscConfigDict(language=request.LANGUAGE_CODE, domain=domain)}
+    return {'misc_config': request.misc_config}
 
 
 def site_name(request):

templates/base.html

@@ -281,8 +281,8 @@
         <div id="content-body">{% block body %}{% endblock %}</div>
     </main>
 
-    {% if i18n_config.announcement %}
-        <div id="announcement">{{ i18n_config.announcement|safe }}</div>
+    {% if misc_config.announcement %}
+        <div id="announcement">{{ misc_config.announcement|safe }}</div>
     {% endif %}
 
     {% block bodyend %}{% endblock %}
@@ -291,8 +291,8 @@
         <span id="footer-content">
             <br>
             <a style="color: #808080" href="https://dmoj.ca">{{ _('proudly powered by **DMOJ**')|markdown('default', strip_paragraphs=True) }}</a> |
-            {% if i18n_config.footer %}
-                {{ i18n_config.footer|safe }} |
+            {% if misc_config.footer %}
+                {{ misc_config.footer|safe }} |
             {% endif %}
             <form action="{{ url('set_language') }}" method="post" style="display: inline">
                 {% csrf_token %}

templates/home.html

@@ -1,12 +1,12 @@
 {% extends "blog/list.html" %}
 {% block before_posts %}
-    {% if i18n_config.home_page_top %}
-        {{ render_django(i18n_config.home_page_top, request=request, user_count=user_count, problem_count=problem_count, submission_count=submission_count, language_count=language_count, perms=perms) }}
+    {% if misc_config.home_page_top %}
+        {{ render_django(misc_config.home_page_top, request=request, user_count=user_count, problem_count=problem_count, submission_count=submission_count, language_count=language_count, perms=perms) }}
     {% endif %}
 {% endblock %}
 {% block meta %}
-    {% if i18n_config.meta_description %}
-        <meta name="description" content="{{ i18n_config['meta_description'] }}">
+    {% if misc_config.meta_description %}
+        <meta name="description" content="{{ misc_config['meta_description'] }}">
     {% endif %}
     <script type="application/ld+json">
         {