Reduce the number of SQL queries used in the "Get Checks" API call

CHANGELOG.md

@@ -8,6 +8,7 @@ All notable changes to this project will be documented in this file.
 - Update API to allow specifying channels by names (#440)
 - When saving a phone number, remove any invisible unicode characers
 - Update the read-only dashboard's CSS for better mobile support (#442)
+- Reduce the number of SQL queries used in the "Get Checks" API call
 
 ## v1.17.0 - 2020-10-14
 

hc/api/models.py

@@ -205,8 +205,10 @@ class Check(models.Model):
     def channels_str(self):
         """ Return a comma-separated string of assigned channel codes. """
 
-        codes = self.channel_set.order_by("code").values_list("code", flat=True)
-        return ",".join(map(str, codes))
+        # self.channel_set may already be prefetched.
+        # Sort in python to make sure we do't run additional queries
+        codes = [str(channel.code) for channel in self.channel_set.all()]
+        return ",".join(sorted(codes))
 
     @property
     def unique_key(self):

hc/api/tests/test_list_checks.py

@@ -37,7 +37,13 @@ class ListChecksTestCase(BaseTestCase):
         return self.client.get("/api/v1/checks/", HTTP_X_API_KEY="X" * 32)
 
     def test_it_works(self):
-        r = self.get()
+        # Expect 3 queries:
+        # * check API key
+        # * retrieve checks
+        # * retrieve  channel codes
+        with self.assertNumQueries(3):
+            r = self.get()
+
         self.assertEqual(r.status_code, 200)
         self.assertEqual(r["Access-Control-Allow-Origin"], "*")
 
@@ -148,7 +154,10 @@ class ListChecksTestCase(BaseTestCase):
         self.project.api_key_readonly = "R" * 32
         self.project.save()
 
-        r = self.client.get("/api/v1/checks/", HTTP_X_API_KEY="R" * 32)
+        # Expect a query to check the API key, and a query to retrieve checks
+        with self.assertNumQueries(2):
+            r = self.client.get("/api/v1/checks/", HTTP_X_API_KEY="R" * 32)
+
         self.assertEqual(r.status_code, 200)
 
         # When using readonly keys, the ping URLs should not be exposed:

hc/api/views.py

@@ -162,7 +162,8 @@ def _update(check, spec):
 @authorize_read
 def get_checks(request):
     q = Check.objects.filter(project=request.project)
-    q = q.prefetch_related("channel_set")
+    if not request.readonly:
+        q = q.prefetch_related("channel_set")
 
     tags = set(request.GET.getlist("tag"))
     for tag in tags: