Simplify stock configuration in existing variant overrides

db/migrate/20181128054803_simplify_variant_override_on_demand_and_count_on_hand.rb

@@ -0,0 +1,29 @@
+# This simplifies variant overrides to have only the following combinations:
+#
+#    on_demand | count_on_hand
+#   -----------+---------------
+#    true      | nil
+#    false     | set
+#    nil       | nil
+#
+# Refer to the table {here}[https://github.com/openfoodfoundation/openfoodnetwork/issues/3067] for
+# the effect of different variant and variant override stock configurations.
+#
+# Furthermore, this will allow all existing variant overrides to satisfy the newly added model
+# validation rules.
+class SimplifyVariantOverrideOnDemandAndCountOnHand < ActiveRecord::Migration
+  def up
+    # When on_demand is nil but count_on_hand is set, force limited stock.
+    VariantOverride.where(on_demand: nil).where("count_on_hand IS NOT NULL")
+      .update_all(on_demand: false)
+
+    # Clear count_on_hand if forcing on demand.
+    VariantOverride.where(on_demand: true).update_all(count_on_hand: nil)
+
+    # When on_demand is false but count on hand is not specified, set this to use producer stock
+    # settings.
+    VariantOverride.where(on_demand: false, count_on_hand: nil).update_all(on_demand: nil)
+  end
+
+  def down; end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20181123012635) do
+ActiveRecord::Schema.define(:version => 20181128054803) do
 
   create_table "account_invoices", :force => true do |t|
     t.integer  "user_id",    :null => false