fix: add Product.default_vendor_item convenience property

corepos/db/office_op/model.py

@@ -583,6 +583,32 @@ class Product(common.ProductBase, Base):
         creator=lambda lc: ProductLikeCode(like_code=lc),
     )
 
+    vendor_items = orm.relationship(
+        'VendorItem',
+        back_populates='product',
+        primaryjoin='VendorItem.upc == Product.upc',
+        foreign_keys='VendorItem.upc',
+        order_by='VendorItem.vendor_item_id',
+        doc="""
+        List of :class:`VendorItem` records for this product.
+        """)
+
+    @property
+    def default_vendor_item(self):
+        """
+        Returns the "default" vendor item record.  This will
+        correspond to the :attr:`default_vendor` if possible.
+
+        :rtype: :class:`VendorItem` or ``None``
+        """
+        if self.default_vendor:
+            for item in self.vendor_items:
+                if item.vendor_id == self.default_vendor.id:
+                    return item
+
+        if self.vendor_items:
+            return self.vendor_items[0]
+
     @property
     def full_description(self):
         fields = ['brand', 'description', 'size']
@@ -732,17 +758,12 @@ class VendorItem(Base):
     upc = sa.Column(sa.String(length=13), nullable=False)
     product = orm.relationship(
         Product,
+        back_populates='vendor_items',
         primaryjoin=Product.upc == upc,
         foreign_keys=[upc],
         doc="""
         Reference to the :class:`Product` to which this record applies.
-        """,
-        backref=orm.backref(
-            'vendor_items',
-            order_by=vendor_item_id,
-            doc="""
-            List of :class:`VendorItem` records for this product.
-            """))
+        """)
 
     brand = sa.Column(sa.String(length=50), nullable=True)