Downgrade SQLite upserts to 'update if exists' + add 3.9-dev to travis vers

Unfortunately, SQLite upserts (`ON CONFLICT(name) DO UPDATE xxx`) are a rather new feature (released as of SQLite 3.24.0 2018-06-04),
and it appears that the latest SQLite3 version in Ubuntu 18.04 (Bionic)'s repos is 3.22.0 - meaning that upserts are likely to be unusable
on many systems.

Due to this issue, upsert statements in `SqliteCacheManager` and `AsyncSqliteCacheManager` have been replaced with standard INSERT statements,
and the `update_cache_key` method (in both sync and async classes) now uses a standard `UPDATE` statement, which should work on all systems.

Additionally, `3.9-dev` has now been added to `.travis.yml`, but marked with `allow_failures` to avoid bugs in 3.9 (or problems with third-party libraries
that haven't yet been patched to work with 3.9) causing the travis build to fail.

Author: Someguy123

.travis.yml

@@ -8,17 +8,17 @@ python:
   - "3.6"
   - "3.7"
   - "3.8"
+  - "3.9-dev"
   - "nightly"
 jobs:
   allow_failures:
     # Sometimes nightly builds are broken, or contain breaking changes that affect dependencies we have
     # no control over. Thus we don't want a failed nightly run to cause Travis to consider the build broken.
     - python: 'nightly'
+    - python: '3.9-dev'
 before_install:
-  - sudo apt remove -y sqlite3
-  - sudo apt-add-repository -y ppa:travis-ci/sqlite3
   - sudo apt-get update -qy
-  - sudo apt-get -y install sqlite3
+  - sudo apt-get install -qy sqlite3
   - sudo apt-get install -qy iputils-ping
   - "sudo rsync -avh 'rsync://files.privex.io/cdn/extras/GeoIP/*.mmdb' /usr/share/GeoIP/"
 install:

privex/helpers/cache/post_deps.py

@@ -125,19 +125,22 @@ def cache_key_exists(self, name: str) -> bool:
 
     def insert_cache_key(self, name: str, value: Any, expires_secs: Number = None, expires_at: Union[Number, datetime] = None):
         expires_at = self._calc_expires(expires_at=expires_at, expires_secs=expires_secs)
-        log.debug("Inserting/updating cache key '%s' with expires_at = '%s' and value: %s", name, expires_at, value)
+        log.debug("Inserting cache key '%s' with expires_at = '%s' and value: %s", name, expires_at, value)
+        # return self.action(
+        #     "INSERT INTO pvcache (name, value, expires_at) VALUES (?, ?, ?) "
+        #     "ON CONFLICT(name) DO UPDATE SET value=?,expires_at=?;",
+        #     (name, value, expires_at, value, expires_at)
+        # )
         return self.action(
-            "INSERT INTO pvcache (name, value, expires_at) VALUES (?, ?, ?) "
-            "ON CONFLICT(name) DO "
-            "UPDATE SET value=?,expires_at=?;",
-            (name, value, expires_at, value, expires_at)
+            "INSERT INTO pvcache (name, value, expires_at) VALUES (?, ?, ?);",
+            (name, value, expires_at)
         )
 
     def update_cache_key(self, name: str, value: Any, expires_secs: Number = None, expires_at: Union[Number, datetime] = None):
-        # expires_at = self._calc_expires(expires_at=expires_at, expires_secs=expires_secs)
+        expires_at = self._calc_expires(expires_at=expires_at, expires_secs=expires_secs)
         log.debug("Updating cache key '%s' with expires_at = '%s' and value: %s", name, expires_at, value)
-        return self.insert_cache_key(name, value, expires_at=expires_at, expires_secs=expires_secs)
-        # return self.action("UPDATE pvcache SET value = ?, expires_at = ? WHERE name = ?;", (value, name, expires_at))
+        # return self.insert_cache_key(name, value, expires_at=expires_at, expires_secs=expires_secs)
+        return self.action("UPDATE pvcache SET value = ?, expires_at = ? WHERE name = ?;", (value, expires_at, name))
 
     def set_cache_key(self, name: str, value: Any, expires_secs: Number = None, expires_at: Union[Number, datetime] = None):
         # expires_at = self._calc_expires(expires_at=expires_at, expires_secs=expires_secs)
@@ -225,19 +228,24 @@ async def cache_key_exists(self, name: str) -> bool:
 
         async def insert_cache_key(self, name: str, value: Any, expires_secs: Number = None, expires_at: Union[Number, datetime] = None):
             expires_at = self._calc_expires(expires_at=expires_at, expires_secs=expires_secs)
-            log.debug("Inserting/updating cache key '%s' with expires_at = '%s' and value: %s", name, expires_at, value)
+            log.debug("Inserting cache key '%s' with expires_at = '%s' and value: %s", name, expires_at, value)
+            # return await await_if_needed(self.action(
+            #     "INSERT INTO pvcache (name, value, expires_at) VALUES (?, ?, ?) "
+            #     "ON CONFLICT(name) DO UPDATE SET value=?,expires_at=?;",
+            #     (name, value, expires_at, value, expires_at)
+            # ))
             return await await_if_needed(self.action(
-                "INSERT INTO pvcache (name, value, expires_at) VALUES (?, ?, ?) "
-                "ON CONFLICT(name) DO "
-                "UPDATE SET value=?,expires_at=?;",
-                (name, value, expires_at, value, expires_at)
+                "INSERT INTO pvcache (name, value, expires_at) VALUES (?, ?, ?);",
+                (name, value, expires_at)
             ))
 
         async def update_cache_key(self, name: str, value: Any, expires_secs: Number = None, expires_at: Union[Number, datetime] = None):
-            # expires_at = self._calc_expires(expires_at=expires_at, expires_secs=expires_secs)
+            expires_at = self._calc_expires(expires_at=expires_at, expires_secs=expires_secs)
             log.debug("Updating cache key '%s' with expires_at = '%s' and value: %s", name, expires_at, value)
-            return await self.insert_cache_key(name, value, expires_at=expires_at, expires_secs=expires_secs)
-            # return self.action("UPDATE pvcache SET value = ?, expires_at = ? WHERE name = ?;", (value, name, expires_at))
+            # return await self.insert_cache_key(name, value, expires_at=expires_at, expires_secs=expires_secs)
+            return await await_if_needed(
+                self.action("UPDATE pvcache SET value = ?, expires_at = ? WHERE name = ?;", (value, expires_at, name))
+            )
 
         async def set_cache_key(self, name: str, value: T, expires_secs: Number = None, expires_at: Union[Number, datetime] = None) -> T:
             expires_at = self._calc_expires(expires_at=expires_at, expires_secs=expires_secs)