Implement get_or_create functionality for the host endpoint

This commit essentially makes it so the "unique together" constraint
for host.name -> play.id is enforced through a get_or_create approach
instead.

Change-Id: I9b9c015fa2f4dec4d99f051fa102fd422263fe0f

ara/api/serializers.py

@@ -112,6 +112,23 @@ class HostSerializer(serializers.ModelSerializer):
 
     facts = CompressedObjectField(default=zlib.compress(json.dumps({}).encode('utf8')))
 
+    def get_unique_together_validators(self):
+        '''
+        Hosts have a "unique together" constraint for host.name and play.id.
+        We want to have a "get_or_create" facility and in order to do that, we
+        must manage the validation during the creation, not before.
+        Overriding this method effectively disables this validator.
+        '''
+        return []
+
+    def create(self, validated_data):
+        host, created = models.Host.objects.get_or_create(
+            name=validated_data['name'],
+            play=validated_data['play'],
+            defaults=validated_data
+        )
+        return host
+
 
 class ResultSerializer(serializers.ModelSerializer):
     class Meta:

ara/api/tests/test_host.py

@@ -85,6 +85,28 @@ class HostTestCase(APITestCase):
         self.assertEqual(201, request.status_code)
         self.assertEqual(1, models.Host.objects.count())
 
+    def test_post_same_host_for_a_play(self):
+        play = factories.PlayFactory()
+        self.assertEqual(0, models.Host.objects.count())
+        request = self.client.post('/api/v1/hosts/', {
+            'name': 'create',
+            'play': play.id,
+            'ok': 1
+        })
+        self.assertEqual(201, request.status_code)
+        self.assertEqual(1, models.Host.objects.count())
+        self.assertEqual(1, request.data['ok'])
+
+        request = self.client.post('/api/v1/hosts/', {
+            'name': 'create',
+            'play': play.id,
+            'ok': 2
+        })
+        self.assertEqual(201, request.status_code)
+        self.assertEqual(1, models.Host.objects.count())
+        # This isn't expected to update the count for 'ok', it's not a patch
+        self.assertEqual(1, request.data['ok'])
+
     def test_partial_update_host(self):
         host = factories.HostFactory()
         self.assertNotEqual(1, host.ok)