raising custom exceptions

ordr3/repo.py

@@ -3,10 +3,17 @@
 import abc
 
 from sqlalchemy import func
+from sqlalchemy.orm.exc import NoResultFound
 
 from . import models
 
 
+class RepoItemNotFound(StopIteration):
+    """ repo error for a not found item """
+
+    pass
+
+
 class AbstractOrderRepository(abc.ABC):
     """ Abstract base class for a datastore """
 
@@ -63,9 +70,14 @@ class SqlAlchemyRepository(AbstractOrderRepository):
 
     def get_order(self, reference):
         """ get an order from the database by primary key """
+        try:
             return (
-            self.session.query(models.OrderItem).filter_by(id=reference).one()
+                self.session.query(models.OrderItem)
+                .filter_by(id=reference)
+                .one()
             )
+        except NoResultFound as exc:
+            raise RepoItemNotFound from exc
 
     def list_orders(self):
         """ list orders orderd by date, descending """
@@ -81,21 +93,34 @@ class SqlAlchemyRepository(AbstractOrderRepository):
 
     def get_user(self, reference):
         """ get a user from the database by primary key """
-        return self.session.query(models.User).filter_by(id=reference).one()
+        try:
+            return (
+                self.session.query(models.User).filter_by(id=reference).one()
+            )
+        except NoResultFound as exc:
+            raise RepoItemNotFound from exc
 
     def get_user_by_username(self, reference):
         """ get a user from the database by username """
+        try:
             return (
-            self.session.query(models.User).filter_by(username=reference).one()
+                self.session.query(models.User)
+                .filter_by(username=reference)
+                .one()
             )
+        except NoResultFound as exc:
+            raise RepoItemNotFound from exc
 
     def get_user_by_email(self, reference):
         """ get a user from the database by email """
+        try:
             return (
                 self.session.query(models.User)
                 .filter(func.lower(models.User.email) == func.lower(reference))
                 .one()
             )
+        except NoResultFound as exc:
+            raise RepoItemNotFound from exc
 
     def list_users(self):
         """ list users orderd by username """