Don't log package updates in Python when we have DB trigger support

This adds a helper method to find the database engine in use, and then
skips code we shouldn't execute if we are doing this another way.

Note that this helper method could be useful for backend-specific code
paths elsewhere, such as custom SQL being called or lack of StdDev() in
sqlite3 out of the box.

Signed-off-by: Dan McGee <dan@archlinux.org>

2 files changed, 24 insertions, 2 deletions

diff --git a/main/utils.py b/main/utils.py
index b7cb19f4..879abfb9 100644
--- a/main/utils.py
+++ b/main/utils.py
@@ -8,6 +8,7 @@ import hashlib
 from pytz import utc
 
 from django.core.cache import cache
+from django.db import connections, router
 
 
 CACHE_TIMEOUT = 1800
@@ -106,6 +107,16 @@ def set_created_field(sender, **kwargs):
         obj.created = utc_now()
 
 
+def database_vendor(model, mode='read'):
+    if mode == 'read':
+        database = router.db_for_read(model)
+    elif mode == 'write':
+        database = router.db_for_write(model)
+    else:
+        raise Exception('Invalid database mode specified')
+    return connections[database].vendor
+
+
 def groupby_preserve_order(iterable, keyfunc):
     '''Take an iterable and regroup using keyfunc to determine whether items
     belong to the same group. The order of the iterable is preserved and
diff --git a/packages/models.py b/packages/models.py
index 2f03a28b..45ff3c08 100644
--- a/packages/models.py
+++ b/packages/models.py
@@ -6,7 +6,7 @@ from django.contrib.admin.models import ADDITION, CHANGE, DELETION
 from django.contrib.auth.models import User
 
 from main.models import Arch, Repo, Package
-from main.utils import set_created_field
+from main.utils import set_created_field, database_vendor
 
 
 class PackageRelation(models.Model):
@@ -207,7 +207,12 @@ class UpdateManager(models.Manager):
     def log_update(self, old_pkg, new_pkg):
         '''Utility method to help log an update. This will determine the type
         based on how many packages are passed in, and will pull the relevant
-        necesary fields off the given packages.'''
+        necesary fields off the given packages.
+        Note that in some cases, this is a no-op if we know this database type
+        supports triggers to add these rows instead.'''
+        if database_vendor(Package, 'write') in ('sqlite', 'postgresql'):
+            # we log updates using database triggers for these backends
+            return
         update = Update()
         if new_pkg:
             update.action_flag = ADDITION
@@ -222,6 +227,12 @@ class UpdateManager(models.Manager):
         if old_pkg:
             if new_pkg:
                 update.action_flag = CHANGE
+                # ensure we should even be logging this
+                if (old_pkg.pkgver == new_pkg.pkgver and
+                        old_pkg.pkgrel == new_pkg.pkgrel and
+                        old_pkg.epoch == new_pkg.epoch):
+                    # all relevant fields were the same; e.g. a force update
+                    return
             else:
                 update.action_flag = DELETION
                 update.arch = old_pkg.arch