Checks that the database and the cache are compatible.

cachalot/apps.py

@@ -1,8 +1,45 @@
 from django.apps import AppConfig
+from django.conf import settings
+from django.core.checks import register, Tags, Error, Warning
 
 from .monkey_patch import patch
 
 
+VALID_DATABASE_ENGINES = {
+    'django.db.backends.sqlite3',
+    'django.db.backends.postgresql_psycopg2',
+    'django.db.backends.mysql',
+}
+
+
+VALID_CACHE_BACKENDS = {
+    'django.core.cache.backends.locmem.LocMemCache',
+    'django.core.cache.backends.filebased.FileBasedCache',
+    'django_redis.cache.RedisCache',
+    'django.core.cache.backends.memcached.MemcachedCache',
+    'django.core.cache.backends.memcached.PyLibMCCache',
+}
+
+
+@register(Tags.compatibility)
+def check_compatibility(app_configs, **kwargs):
+    errors = []
+    for setting, k, valid_values in (
+            (settings.DATABASES, 'ENGINE', VALID_DATABASE_ENGINES),
+            (settings.CACHES, 'BACKEND', VALID_CACHE_BACKENDS)):
+        for alias, d in setting.items():
+            value = d[k]
+            if value not in valid_values:
+                error_class = Error if alias == 'default' else Warning
+                errors.append(
+                    error_class(
+                        '`%s` is not compatible with django-cachalot.' % value,
+                        id='cachalot.E001',
+                    )
+                )
+    return errors
+
+
 class CachalotConfig(AppConfig):
     name = 'cachalot'
     patched = False