[Patchew-devel] [PATCH] models: avoid IntegrityError when clearing log property

[Paolo Bonzini]

Result's log property provides some magic to hide the existence of
the LogEntry table (which in turn is only there to optimize access
to results, since the logs are rarely needed).

However, deleting the entry directly in the setter does not work,
because at this point the entry is still referenced in the Result
table.  Postgres complains about a foreign key constraint violation
when the setter calls entry.delete().

To fix this, which shows up as an error in the git-reset action,
detect at save time whether the log_entry became None, and if so
delete it _after_ saving the model.  While I am touching the code,
fix the override of save() to correctly pass the arguments to the
superclass.
---
 api/models.py | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/api/models.py b/api/models.py
index e24098b..8ec89b6 100644
--- a/api/models.py
+++ b/api/models.py
@@ -74,11 +74,19 @@ class Result(models.Model):
     def is_running(self):
         return self.status == self.RUNNING
 
-    def save(self):
+    def save(self, *args, **kwargs):
         self.last_update = datetime.datetime.utcnow()
         old_result = Result.objects.filter(pk=self.pk).first()
         old_status = old_result.status if old_result else None
-        super(Result, self).save()
+        old_entry = old_result.log_entry if old_result else None
+        super(Result, self).save(*args, **kwargs)
+
+        if self.log_entry is None and old_entry is not None:
+            # Quick way to check if the field was actually saved to the database
+            new_result = Result.objects.filter(pk=self.pk).first()
+            if new_result.log_entry is None:
+                old_entry.delete()
+
         emit_event("ResultUpdate", obj=self.obj,
                    old_status=old_status, result=self)
 
@@ -109,18 +117,15 @@ class Result(models.Model):
 
     @log.setter
     def log(self, value):
-        entry = self.log_entry
         if value is None:
-            if entry is not None:
-                self.log_entry = None
-                entry.delete()
-        else:
-            if entry is None:
-                entry = LogEntry()
-            entry.data = value
-            entry.save()
-            if self.log_entry is None:
-                self.log_entry = entry
+            self.log_entry = None
+            return
+
+        entry = self.log_entry or LogEntry()
+        entry.data = value
+        entry.save()
+        if self.log_entry is None:
+            self.log_entry = entry
 
     def get_log_url(self, request=None):
         if not self.is_completed() or self.renderer is None:
-- 
2.19.1