Query for the current task correctly

Summary:
We don't really make use of `Task.id`, we use `Task.task_id`, which is really `child_id`.
The original logic was broken due to this conclusion; this updates to query for the actual
primary key, and adjusts the tests accordingly.
Once this works, the additional logging will be removed.

Test Plan: Unit

Reviewers: anupc

Reviewed By: anupc

Subscribers: changesbot

Differential Revision: https://tails.corp.dropbox.com/D220573

changes/models/task.py

@@ -46,6 +46,7 @@ class Task(db.Model):
 
     id = Column(GUID, primary_key=True, default=uuid.uuid4)
     task_name = Column(String(128), nullable=False)
+    # TODO: Rename 'task_id' to 'child_id' in code to make things less confusing.
     task_id = Column('child_id', GUID, nullable=False)
     parent_id = Column(GUID)
     status = Column(Enum(Status), nullable=False, default=Status.unknown)

changes/queue/task.py

@@ -439,7 +439,11 @@ def _report_lag(self, first_run_time):
             first_run_time (datetime): When the task started running.
         """
         # type: (datetime) -> None
-        t = Task.query.get(self.task_id)
+        t = Task.query.filter(
+            Task.task_name == self.task_name,
+            Task.task_id == self.task_id,
+            Task.parent_id == self.parent_id
+        ).first()
         # Ensure the task exists, and that the creation and modification date
         # are the same (meaning we're at the first run).
         if t and t.date_created == t.date_modified:

tests/changes/queue/test_task.py

@@ -33,10 +33,11 @@ def test_report_lag(self):
         creation_date = datetime(2016, 8, 12, 17, 42, 27)
         fresh_task = self.create_task(
             task_name='success_task',
+            task_id=UUID('94bec3a1-592d-4734-b84b-55ba0226e5d1'),
             date_created=creation_date,
             status=Status.queued,
         )
-        success_task.task_id = fresh_task.id
+        success_task.task_id = fresh_task.task_id
 
         fake_stats = mock.Mock(spec=Stats)
         with mock.patch.object(statsreporter, 'stats') as get_stats: