Reduce query count when retrieving satisfiers and providers

Django doesn't attach the parent object to the child objects, even when
queried through the related manager. This causes up to 3 extra queries:
one to retrieve the package again, and one each for arch and repo
retrieval.

For a package like archboot, this drops the number of necessary queries
for the package page from 805 to 222 (yes, this is still too high) and
cuts the time spent waiting on the database from 505ms to 262ms.

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

1 files changed, 12 insertions, 8 deletions

diff --git a/packages/models.py b/packages/models.py
index a4095f5..18d57c5 100644
--- a/packages/models.py
+++ b/packages/models.py
@@ -349,14 +349,16 @@ class RelatedToBase(models.Model):
     name = models.CharField(max_length=255, db_index=True)
     version = models.CharField(max_length=255, default='')
 
-    def get_best_satisfier(self):
+    def get_best_satisfier(self, main_pkg=None):
         '''Find a satisfier for this related package that best matches the
         given criteria. It will not search provisions, but will find packages
         named and matching repo characteristics if possible.'''
+        if main_pkg is None:
+            main_pkg = self.pkg
         pkgs = Package.objects.normal().filter(pkgname=self.name)
-        if not self.pkg.arch.agnostic:
+        if not main_pkg.arch.agnostic:
             # make sure we match architectures if possible
-            arches = self.pkg.applicable_arches()
+            arches = main_pkg.applicable_arches()
             pkgs = pkgs.filter(arch__in=arches)
         # if we have a comparison operation, make sure the packages we grab
         # actually satisfy the requirements
@@ -376,25 +378,27 @@ class RelatedToBase(models.Model):
         pkg = pkgs[0]
         # prevents yet more DB queries, these lists should be short;
         # after each grab the best available in case we remove all entries
-        pkgs = [p for p in pkgs if p.repo.staging == self.pkg.repo.staging]
+        pkgs = [p for p in pkgs if p.repo.staging == main_pkg.repo.staging]
         if len(pkgs) > 0:
             pkg = pkgs[0]
 
-        pkgs = [p for p in pkgs if p.repo.testing == self.pkg.repo.testing]
+        pkgs = [p for p in pkgs if p.repo.testing == main_pkg.repo.testing]
         if len(pkgs) > 0:
             pkg = pkgs[0]
 
         return pkg
 
-    def get_providers(self):
+    def get_providers(self, main_pkg=None):
         '''Return providers of this related package. Does *not* include exact
         matches as it checks the Provision names only, use get_best_satisfier()
         instead for exact matches.'''
+        if main_pkg is None:
+            main_pkg = self.pkg
         pkgs = Package.objects.normal().filter(
                 provides__name=self.name).order_by().distinct()
-        if not self.pkg.arch.agnostic:
+        if not main_pkg.arch.agnostic:
             # make sure we match architectures if possible
-            arches = self.pkg.applicable_arches()
+            arches = main_pkg.applicable_arches()
             pkgs = pkgs.filter(arch__in=arches)
 
         # If we have a comparison operation, make sure the packages we grab