Rely on database unique constraints (#248)

PR #245 updated the validators to check for duplicate usernames and
emails by running a query before posting the data. Let's rely on the
database indexes instead, which is more robust. This builds on top of
PR #245's tests to verify the functionality.

src/authentication/basic_auth.py

@@ -16,7 +16,6 @@ def validate(self, data):
             raise ValidationError("A required field was not found.")
 
         self.validate_email(data["email"])
-        self.check_email_or_username_in_use(email=data["email"], username=data["username"])
         if len(data["username"]) > 36:
             raise ValidationError("username_too_long")
 

src/authentication/providers.py

@@ -30,10 +30,6 @@ def validate_email(self, email):
         email_validator = EmailValidator()
         email_validator(email)
 
-    def check_email_or_username_in_use(self, email=None, username=None):
-        if get_user_model().objects.filter(username__iexact=username) or get_user_model().objects.filter(email=email):
-            raise ValidationError("email_or_username_in_use")
-
 
 class LoginProvider(Provider, abc.ABC):  # pragma: no cover
     type = "login"

src/authentication/views.py

@@ -87,6 +87,14 @@ class RegistrationView(CreateAPIView):
     def dispatch(self, *args, **kwargs):
         return super(RegistrationView, self).dispatch(*args, **kwargs)
 
+    def create(self, request, *args, **kwargs):
+        try:
+            return super().create(request, *args, **kwargs)
+        except IntegrityError:
+            # If we need granularity to see whether email or username is in used here,
+            # check the constraint name that is returned.
+            return FormattedResponse(m="email_or_username_in_use", status=HTTP_400_BAD_REQUEST)
+
 
 class LogoutView(APIView):
     permission_classes = (permissions.IsAuthenticated & ~IsBot,)

src/team/serializers.py

@@ -101,20 +101,18 @@ class Meta:
         fields = ["id", "is_visible", "name", "owner", "password"]
         read_only_fields = ["id", "is_visible", "owner"]
 
-    def validate(self, attrs):
-        if Team.objects.filter(name__iexact=self.initial_data["name"]):
-            raise ValidationError("team_name_in_use")
-        return super(CreateTeamSerializer, self).validate(attrs)
-
     def create(self, validated_data):
-        name = validated_data["name"]
-        password = validated_data["password"]
-        team = Team.objects.create(
-            name=name,
-            password=password,
-            owner=self.context["request"].user,
-        )
-        self.context["request"].user.team = team
-        self.context["request"].user.save()
-        team_create.send(sender=self.__class__, team=team)
-        return team
+        try:
+            name = validated_data["name"]
+            password = validated_data["password"]
+            team = Team.objects.create(
+                name=name,
+                password=password,
+                owner=self.context["request"].user,
+            )
+            self.context["request"].user.team = team
+            self.context["request"].user.save()
+            team_create.send(sender=self.__class__, team=team)
+            return team
+        except IntegrityError:
+            raise ValidationError("team_name_in_use")