Fix "edit row" logic for ordering batch

previous logic allowed `colander.null` to be passed to batch handler, which
caused an error.  also it allowed editing "all" fields for the row, which we
really don't need to do, so now we just support the order quantities

docs/api/views/purchasing.ordering.rst

@@ -10,4 +10,6 @@
 
    .. autoattribute:: default_handler_spec
 
+   .. automethod:: configure_row_form
+
    .. automethod:: worksheet_update

tailbone/views/purchasing/batch.py

@@ -922,8 +922,18 @@ class PurchasingBatchView(BatchMasterView):
 
         if batch.mode == self.enum.PURCHASE_BATCH_MODE_ORDERING:
 
-            # let handler update data, per given order quantities
+            # figure out which values need updating
-            data = self.form_deserialized
+            form_data = self.form_deserialized
+            data = {}
+            for key in ('cases_ordered', 'units_ordered'):
+                if key in form_data:
+                    # this is really to convert/avoid colander.null, but the
+                    # handler method also assumes that if we pass a value, it
+                    # will not be None
+                    data[key] = form_data[key] or 0
+            if data:
+
+                # let handler do the actual updating
                 self.handler.update_row_quantity(row, **data)
 
         else: # *not* ordering mode

tailbone/views/purchasing/ordering.py

@@ -2,7 +2,7 @@
 ################################################################################
 #
 #  Rattail -- Retail Software Framework
-#  Copyright © 2010-2019 Lance Edgar
+#  Copyright © 2010-2020 Lance Edgar
 #
 #  This file is part of Rattail.
 #
@@ -121,6 +121,23 @@ class OrderingBatchView(PurchasingBatchView):
         'status_code',
     ]
 
+    row_form_fields = [
+        'item_entry',
+        'item_id',
+        'upc',
+        'product',
+        'brand_name',
+        'description',
+        'size',
+        'case_quantity',
+        'cases_ordered',
+        'units_ordered',
+        'po_line_number',
+        'po_unit_cost',
+        'po_total_calculated',
+        'status_code',
+    ]
+
     order_form_header_columns = [
         "UPC",
         "Brand",
@@ -147,6 +164,28 @@ class OrderingBatchView(PurchasingBatchView):
         kwargs['notes_to_vendor'] = batch.notes_to_vendor
         return kwargs
 
+    def configure_row_form(self, f):
+        """
+        Supplements the default logic as follows:
+
+        When editing, only these fields allow changes; all others are made
+        read-only:
+
+        * ``cases_ordered``
+        * ``units_ordered``
+        """
+        super(OrderingBatchView, self).configure_row_form(f)
+
+        # when editing, only certain fields should allow changes
+        if self.editing:
+            editable_fields = [
+                'cases_ordered',
+                'units_ordered',
+            ]
+            for field in f.fields:
+                if field not in editable_fields:
+                    f.set_readonly(field)
+
     def worksheet(self):
         """
         View for editing batch row data as an order form worksheet.