fix: improve behavior when deleting a Standard Quantity

src/wuttafarm/db/model/quantities.py

@@ -204,7 +204,12 @@ class QuantityMixin:
 
     @declared_attr
     def quantity(cls):
-        return orm.relationship(Quantity)
+        return orm.relationship(
+            Quantity,
+            single_parent=True,
+            cascade="all, delete-orphan",
+            cascade_backrefs=False,
+        )
 
     def render_as_text(self, config=None):
         return self.quantity.render_as_text(config)

src/wuttafarm/web/views/farmos/quantities.py

@@ -26,6 +26,7 @@ View for farmOS Quantity Types
 import datetime
 
 import colander
+import requests
 
 from wuttaweb.forms.schema import WuttaDateTime
 from wuttaweb.forms.widgets import WuttaDateTimeWidget
@@ -204,9 +205,15 @@ class QuantityMasterView(FarmOSMasterView):
         return qty["value"]["decimal"]
 
     def get_instance(self):
-        quantity = self.farmos_client.resource.get_id(
-            "quantity", self.farmos_quantity_type, self.request.matchdict["uuid"]
-        )
+        # TODO: this pattern should be repeated for other views
+        try:
+            quantity = self.farmos_client.resource.get_id(
+                "quantity", self.farmos_quantity_type, self.request.matchdict["uuid"]
+            )
+        except requests.HTTPError as exc:
+            if exc.response.status_code == 404:
+                raise self.notfound()
+
         self.raw_json = quantity
 
         data = self.normalize_quantity(quantity["data"])