Handle missing SubscriptionItem.quantity on metered plans

Fixes dj-stripe#865

HISTORY.rst

@@ -13,6 +13,7 @@ This is a bugfix-only version:
   At some point 2018 Stripe silently changed the ID used for test events and
   ``evt_00000000000000`` is not used anymore.
 - Fixed OperationalError seen in migration 0003 on postgres (#850).
+- Fixup missing ``SubscriptionItem.quantity`` on Plans with ``usage_type="metered"`` (#865).
 
 2.0.0 (2019-03-01)
 ------------------

djstripe/models/billing.py

@@ -1199,6 +1199,7 @@ class SubscriptionItem(StripeModel):
 		related_name="subscription_items",
 		help_text="The plan the customer is subscribed to.",
 	)
+	# TODO - quantity should be nullable, since it's not set for metered plans
 	quantity = models.PositiveIntegerField(
 		help_text=("The quantity of the plan to which the customer should be subscribed.")
 	)
@@ -1209,6 +1210,14 @@ class SubscriptionItem(StripeModel):
 		help_text="The subscription this subscription item belongs to.",
 	)
 
+	@classmethod
+	def _manipulate_stripe_object_hook(cls, data):
+		# for metered plans quantity isn't set, so should be nullable
+		# arguably this should default to 1 instead of 0 (to match subscription)
+		data["quantity"] = data.get("quantity") or 0
+
+		return data
+
 
 class UsageRecord(StripeModel):
 	"""

tests/__init__.py

@@ -770,6 +770,27 @@ def capture(self):
 	],
 }
 
+FAKE_PLAN_METERED = {
+	"id": "plan_fakemetered",
+	"object": "plan",
+	"active": True,
+	"aggregate_usage": "sum",
+	"amount": 200,
+	"billing_scheme": "per_unit",
+	"created": 1552632817,
+	"currency": "usd",
+	"interval": "month",
+	"interval_count": 1,
+	"livemode": False,
+	"metadata": {},
+	"nickname": "Sum Metered Plan",
+	"tiers": None,
+	"tiers_mode": None,
+	"transform_usage": None,
+	"trial_period_days": None,
+	"usage_type": "metered",
+}
+
 
 class SubscriptionDict(dict):
 	def __setattr__(self, name, value):
@@ -778,7 +799,7 @@ def __setattr__(self, name, value):
 
 		# Special case for plan
 		if name == "plan":
-			for plan in [FAKE_PLAN, FAKE_PLAN_II]:
+			for plan in [FAKE_PLAN, FAKE_PLAN_II, FAKE_TIER_PLAN, FAKE_PLAN_METERED]:
 				if value == plan["id"]:
 					value = plan
 
@@ -925,6 +946,43 @@ def save(self, idempotency_key=None):
 )
 
 
+FAKE_SUBSCRIPTION_METERED = SubscriptionDict(
+	{
+		"id": "sub_1rn1dp7WgjMtx9",
+		"object": "subscription",
+		"application_fee_percent": None,
+		"billing": "charge_automatically",
+		"cancel_at_period_end": False,
+		"canceled_at": None,
+		"current_period_end": 1441907581,
+		"current_period_start": 1439229181,
+		"customer": "cus_6lsBvm5rJ0zyHc",
+		"discount": None,
+		"ended_at": None,
+		"metadata": {},
+		"items": {
+			"data": [
+				{
+					"created": 1441907581,
+					"id": "si_UXYmKmJp6aWTw6",
+					"metadata": {},
+					"object": "subscription_item",
+					"plan": deepcopy(FAKE_PLAN_METERED),
+					"subscription": "sub_1rn1dp7WgjMtx9",
+				}
+			]
+		},
+		"plan": deepcopy(FAKE_PLAN_METERED),
+		"quantity": 1,
+		"start": 1439229181,
+		"status": "active",
+		"tax_percent": None,
+		"trial_end": None,
+		"trial_start": None,
+	}
+)
+
+
 class Sources(object):
 	def __init__(self, card_fakes):
 		self.card_fakes = card_fakes

tests/test_plan.py

@@ -9,10 +9,13 @@
 from django.test import TestCase
 
 from djstripe.admin import PlanAdmin
+from djstripe.enums import PlanUsageType
 from djstripe.models import Plan
 from djstripe.settings import STRIPE_SECRET_KEY
 
-from . import FAKE_PLAN, FAKE_PLAN_II, FAKE_TIER_PLAN, AssertStripeFksMixin
+from . import (
+	FAKE_PLAN, FAKE_PLAN_II, FAKE_PLAN_METERED, FAKE_TIER_PLAN, AssertStripeFksMixin
+)
 
 
 class TestPlanAdmin(TestCase):
@@ -116,6 +119,18 @@ def test_stripe_tier_plan(self, plan_retrieve_mock):
 			plan, expected_blank_fks={"djstripe.Customer.coupon", "djstripe.Plan.product"}
 		)
 
+	@patch("stripe.Plan.retrieve")
+	def test_stripe_metered_plan(self, plan_retrieve_mock):
+		plan_data = deepcopy(FAKE_PLAN_METERED)
+		plan = Plan.sync_from_stripe_data(plan_data)
+		self.assertEqual(plan.id, plan_data["id"])
+		self.assertEqual(plan.usage_type, PlanUsageType.metered)
+		self.assertIsNotNone(plan.amount)
+
+		self.assert_fks(
+			plan, expected_blank_fks={"djstripe.Customer.coupon", "djstripe.Plan.product"}
+		)
+
 
 class HumanReadablePlanTest(TestCase):
 	def test_human_readable_free_usd_daily(self):

tests/test_subscription.py

@@ -14,8 +14,8 @@
 from djstripe.models import Plan, Subscription
 
 from . import (
-	FAKE_CUSTOMER, FAKE_CUSTOMER_II, FAKE_PLAN, FAKE_PLAN_II,
-	FAKE_SUBSCRIPTION, FAKE_SUBSCRIPTION_CANCELED,
+	FAKE_CUSTOMER, FAKE_CUSTOMER_II, FAKE_PLAN, FAKE_PLAN_II, FAKE_PLAN_METERED,
+	FAKE_SUBSCRIPTION, FAKE_SUBSCRIPTION_CANCELED, FAKE_SUBSCRIPTION_METERED,
 	FAKE_SUBSCRIPTION_MULTI_PLAN, AssertStripeFksMixin, datetime_to_unix
 )
 
@@ -464,3 +464,46 @@ def test_sync_multi_plan(
 
 		items = subscription.items.all()
 		self.assertEqual(2, len(items))
+
+		self.assert_fks(
+			subscription,
+			expected_blank_fks={
+				"djstripe.Customer.coupon",
+				"djstripe.Customer.subscriber",
+				"djstripe.Plan.product",
+				"djstripe.Subscription.plan",
+			},
+		)
+
+	@patch("stripe.Plan.retrieve")
+	@patch("stripe.Customer.retrieve", return_value=deepcopy(FAKE_CUSTOMER_II))
+	@patch(
+		"stripe.Subscription.retrieve", return_value=deepcopy(FAKE_SUBSCRIPTION_METERED)
+	)
+	def test_sync_metered_plan(
+		self, subscription_retrieve_mock, customer_retrieve_mock, plan_retrieve_mock
+	):
+		subscription_fake = deepcopy(FAKE_SUBSCRIPTION_METERED)
+		self.assertNotIn(
+			"quantity",
+			subscription_fake["items"]["data"],
+			"Expect Metered plan SubscriptionItem to have no quantity",
+		)
+
+		subscription = Subscription.sync_from_stripe_data(subscription_fake)
+
+		items = subscription.items.all()
+		self.assertEqual(1, len(items))
+
+		item = items[0]
+
+		self.assertEqual(subscription.quantity, 1)
+		# Note that subscription.quantity is 1, but item.quantity isn't set on metered plans,
+		# it probably should be nullable
+		self.assertEqual(item.quantity, 0)
+		self.assertEqual(item.plan.id, FAKE_PLAN_METERED["id"])
+
+		self.assert_fks(
+			subscription,
+			expected_blank_fks={"djstripe.Customer.coupon", "djstripe.Plan.product"},
+		)