Fix conj keys TTL in Redis 7.x

Closes #475

cacheops/lua/cache_thing.lua

@@ -47,16 +47,13 @@ for db_table, disj in pairs(dnfs) do
         redis.call('sadd', conj_key, key)
         -- NOTE: an invalidator should live longer than any key it references.
         --       So we update its ttl on every key if needed.
-        -- REDIS_7
-        redis.call('expire', conj_key, timeout, 'gt')
-        -- /REDIS_7
-        -- REDIS_4
+        -- NOTE: we also can't use "EXPIRE conj_key timeout GT" because it will have no effect on
+        --       newly created and thus involatile conj keys.
         local conj_ttl = redis.call('ttl', conj_key)
         if conj_ttl < timeout then
             -- We set conj_key life with a margin over key life to call expire rarer
             -- And add few extra seconds to be extra safe
             redis.call('expire', conj_key, timeout * 2 + 10)
         end
-        -- /REDIS_4
     end
 end

cacheops/lua/cache_thing_insideout.lua

@@ -28,17 +28,14 @@ for _, conj_key in ipairs(conj_keys) do
     table.insert(stamps, stamp)
     -- NOTE: an invalidator should live longer than any key it references.
     --       So we update its ttl on every key if needed.
-    -- REDIS_7
-    redis.call('expire', conj_key, timeout, 'gt')
-    -- /REDIS_7
-    -- REDIS_4
+    -- NOTE: we also can't use "EXPIRE conj_key timeout GT" because it will have no effect on
+    --       newly created and thus involatile conj keys.
     local conj_ttl = redis.call('ttl', conj_key)
     if conj_ttl < timeout then
         -- We set conj_key life with a margin over key life to call expire rarer
         -- And add few extra seconds to be extra safe
         redis.call('expire', conj_key, timeout * 2 + 10)
     end
-    -- /REDIS_4
 end
 
 -- Write data to cache along with a checksum of the stamps to see if any of them changed

tests/test_low_level.py

@@ -0,0 +1,22 @@
+import pytest
+
+from cacheops.redis import redis_client
+
+from .models import User
+from .utils import BaseTestCase
+
+
+@pytest.fixture()
+def base(db):
+    case = BaseTestCase()
+    case.setUp()
+    yield
+    case.tearDown()
+
+
+def test_ttl(base, django_assert_num_queries):
+    user = User.objects.create(username='Suor')
+    qs = User.objects.cache(timeout=100).filter(pk=user.pk)
+    list(qs)
+    assert 90 <= redis_client.ttl(qs._cache_key()) <= 100
+    assert redis_client.ttl(f'conj:auth_user:id={user.id}') > 100