Use a from_db class method instead of a separate method to always provider a timer's current duration.

core/models.py

@@ -156,11 +156,12 @@ class Timer(models.Model):
     def __str__(self):
         return self.name or 'Timer #{}'.format(self.id)
 
-    def current_duration(self):
-        if self.duration:
-            return self.duration
-        else:
-            return timezone.now() - self.start
+    @classmethod
+    def from_db(cls, db, field_names, values):
+        instance = super(Timer, cls).from_db(db, field_names, values)
+        if not instance.duration:
+            instance.duration = timezone.now() - instance.start
+        return instance
 
     def restart(self):
         """Restart the timer."""

core/templates/core/timer_detail.html

@@ -12,9 +12,9 @@
     <div class="jumbotron text-center{% if not object.active %} text-danger{% endif %}">
 
         <div class="h1" id="timer-status">
-            <span class="timer-hours">{{ object.current_duration|hours }}</span>h
-            <span class="timer-minutes">{{ object.current_duration|minutes }}</span>m
-            <span class="timer-seconds">{{ object.current_duration|seconds }}</span>s
+            <span class="timer-hours">{{ object.duration|hours }}</span>h
+            <span class="timer-minutes">{{ object.duration|minutes }}</span>m
+            <span class="timer-seconds">{{ object.duration|seconds }}</span>s
         </div>
         <p class="lead text-secondary">
             Started {{ object.start }}
@@ -75,7 +75,7 @@
 {% block javascript %}
     {% if object.active %}
         <script type="application/javascript">
-            BabyBuddy.Timer.run('timer-status');
+            BabyBuddy.Timer.run({{ timer.id }}, 'timer-status');
         </script>
     {% endif %}
 {% endblock %}

core/tests/tests_models.py

@@ -152,11 +152,11 @@ class TimerTestCase(TestCase):
         timer.save()
 
         self.assertEqual(
-            timer.current_duration().seconds,
+            timer.duration().seconds,
             timezone.timedelta(minutes=30).seconds)
         timer.stop()
         self.assertEqual(
-            timer.current_duration().seconds,
+            timer.duration().seconds,
             timezone.timedelta(minutes=30).seconds)