Implement shopping cart

src/allmende_payment_system/models.py

@@ -82,6 +82,7 @@ class Area(Base):
 UnitsOfMeasure = typing.Literal[
     "g",
     "kg",
+    "l",
     "piece",
 ]
 
@@ -121,6 +122,10 @@ class Order(Base):
     def is_in_shopping_cart(self):
         return self.account is None
 
+    @property
+    def total_amount(self):
+        return sum(item.total_amount for item in self.items)
+
 
 class OrderItem(Base):
     __tablename__ = TABLE_PREFIX + "order_item"
@@ -130,7 +135,7 @@ class OrderItem(Base):
 
     product_id: Mapped[int] = mapped_column(ForeignKey(TABLE_PREFIX + "product.id"))
     product: Mapped[Product] = relationship("Product")
-    quantity: Mapped[int] = mapped_column(nullable=False)
+    quantity: Mapped[decimal.Decimal] = mapped_column(nullable=False)
     total_amount: Mapped[decimal.Decimal] = mapped_column(
         Numeric(10, 2), nullable=False
     )