diff --git a/app/controllers/quantities_controller.rb b/app/controllers/quantities_controller.rb
index 32e3c87..1808672 100644
--- a/app/controllers/quantities_controller.rb
+++ b/app/controllers/quantities_controller.rb
@@ -47,7 +47,6 @@ class QuantitiesController < ApplicationController
     render_no_content(@quantity) unless @quantity.update(permitted)
 
     @ancestors = @quantity.ancestors
-    @quantity.depth = @ancestors.length
     @self_and_progenies = @quantity.with_progenies
     @before = @self_and_progenies.last.successive
   end
diff --git a/app/models/quantity.rb b/app/models/quantity.rb
index 3d6b52a..ffc5086 100644
--- a/app/models/quantity.rb
+++ b/app/models/quantity.rb
@@ -68,7 +68,7 @@ class Quantity < ApplicationRecord
       numbered.project(
         numbered[Arel.star],
         numbered.cast(numbered[:child_number], 'BINARY').as('path'),
-      ).where(root ? numbered[:id].eq(root.id) : numbered[:parent_id].eq(nil)),
+      ).where(numbered[root ? :id : :parent_id].eq(root)),
       numbered.project(
         numbered[Arel.star],
         arel_table[:path].concat(numbered[:child_number]),
@@ -121,7 +121,7 @@ class Quantity < ApplicationRecord
   end
 
   def with_progenies
-    user.quantities.ordered(root: self).to_a
+    user.quantities.ordered(root: id).to_a
   end
 
   # Return: record with ID `of` with its ancestors, sorted by `depth`