add next & previous methods on Mesure. Untested in all cases.

src/sherlock/models.py

@@ -18,12 +18,16 @@ class Gauge(models.Model):
 
 class Diff(object):
     def __init__(self, mesure_1, mesure_2):
-        self.diff = mesure_1.diff(mesure_2)
+        self.increase = abs(mesure_1.diff(mesure_2))
+        self.delta = abs(mesure_1.moment - mesure_2.moment)
 
 class Mesure(models.Model):
     moment = models.DateTimeField()
     value = models.DecimalField(max_digits=10, decimal_places=4)
-    gauge = models.ForeignKey(Gauge)
+    gauge = models.ForeignKey(Gauge, related_name='mesures')
+
+    def __str__(self):
+        return "{} {}".format(self.moment, self.value)
 
     def diff(self, other_mesure):
         if self.category != other_mesure.category:
@@ -31,9 +35,14 @@ class Mesure(models.Model):
         
         return self.value - other_mesure.value
 
-    def diff_number_of_days(self, other_mesure):
-        max(self.moment, other_mesure.moment) - min(self.moment, other_mesure.moment)
-
     @property
     def category(self):
         return self.gauge.category
+    
+    @property
+    def previous(self):
+        return self.gauge.mesures.filter(moment__lt=self.moment).order_by('-moment')[0]
+    
+    @property
+    def next(self):
+        return self.gauge.mesures.filter(moment__gt=self.moment).order_by('moment')[0]

src/sherlock/tests.py

@@ -36,6 +36,13 @@ class TestGaugeModel(TestCase):
         self.assertEqual(gauge_2, gauges_list[2])
         self.assertEqual(gauge_3, gauges_list[3])
     
+    def test_mesures_related_name(self):
+        cat_water = Category.objects.create(name='eau')
+        gauge_1 = Gauge.objects.create(serial_number='undefined', category=cat_water)
+        self.mesure_1 = Mesure.objects.create(moment=timezone.make_aware(datetime.now()), value=0.001, gauge=gauge_1)
+
+        self.assertEqual(1, len(gauge_1.mesures.all()))
+
 class TestMesureModel(TestCase):
 
     def setUp(self):
@@ -45,8 +52,11 @@ class TestMesureModel(TestCase):
         self.gauge_1 = Gauge.objects.create(serial_number='undefined', category=self.cat_water)
         self.gauge_2 = Gauge.objects.create(serial_number='undefined', category=self.cat_gaz)
         
-        self.mesure_1 = Mesure.objects.create(moment=timezone.make_aware(datetime.now()), value=0.001, gauge=self.gauge_1)
-        self.mesure_2 = Mesure.objects.create(moment=timezone.make_aware(datetime.now()), value=0.002, gauge=self.gauge_2)
+        d1 = timezone.make_aware(datetime(2016, 1, 2))
+        d2 = timezone.make_aware(datetime(2016, 1, 3))
+
+        self.mesure_1 = Mesure.objects.create(moment=d1, value=0.001, gauge=self.gauge_1)
+        self.mesure_2 = Mesure.objects.create(moment=d2, value=0.002, gauge=self.gauge_2)
         self.mesure_3 = Mesure.objects.create(moment=timezone.make_aware(datetime.now()), value=0.003, gauge=self.gauge_1)
         
     def test_category_property(self):        
@@ -60,3 +70,10 @@ class TestMesureModel(TestCase):
 
         with self.assertRaises(Exception):
             mesure_1.diff(mesure_2)
+    
+    def test_previous(self):
+        self.assertEqual(self.mesure_1, self.mesure_2.previous)
+    
+    def test_next(self):
+        self.assertEqual(self.mesure_2, self.mesure_1.next)
+