Add an all_products property to FlagBase

It's common to need to query the fill list of products covered by a
Flag - whether directly, or by being in an included category.

Add an all_products property which does this.

vendor/registrasion/registrasion/models/conditions.py

@@ -5,6 +5,7 @@ from . import inventory
 from django.contrib.auth.models import Group
 from django.core.exceptions import ValidationError
 from django.db import models
+from django.db.models import F, Q
 from django.utils.encoding import python_2_unicode_compatible
 from django.utils.translation import ugettext_lazy as _
 from model_utils.managers import InheritanceManager
@@ -383,10 +384,15 @@ class FlagBase(models.Model):
             ``ENABLE_IF_TRUE`` condition.
 
         products ([inventory.Product, ...]):
-            The Products affected by this flag.
+            The Products affected directly by this flag.
 
         categories ([inventory.Category, ...]):
             The Categories whose Products are affected by this flag.
+
+        all_products ([inventory.Product, ...]):
+            All products affected by this flag, either by being listed directly
+            or by having their category listed.
+
     '''
 
     objects = InheritanceManager()
@@ -439,6 +445,17 @@ class FlagBase(models.Model):
         related_name="flagbase_set",
     )
 
+    @property
+    def all_products(self):
+        all_products = inventory.Product.objects.all()
+        all_products = all_products.filter(
+            (
+                Q(id__in=self.products.all()) |
+                Q(category_id__in=self.categories.all())
+            )
+        )
+        return all_products
+
 
 class TimeOrStockLimitFlag(TimeOrStockLimitCondition, FlagBase):
     ''' Product groupings that can be used to enable a product during a