Validate ancestor_ids instead of raw ancestry column

The builder defines `def ancestry` to return `before_type_cast` for
backwards compatibility. Validating the column meant the validator
received raw strings on all Rails versions. Validating `ancestor_ids`
receives the deserialized array directly.

- Remove `alias_attribute :ancestor_ids` (builder already defines it
  via `read_attribute`, which goes through the Type)
- Guard dirty-tracking methods (`_in_database`, `_before_last_save`)
  with explicit deserialize for Rails < 7.2 compatibility
- `sane_ancestor_ids?` looks up validators on `:ancestor_ids`

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kbrock

lib/ancestry/ancestry_validator.rb

@@ -3,17 +3,16 @@
 module Ancestry
   class AncestryValidator < ActiveModel::EachValidator
     def validate_each(record, attribute, value)
-      ids = value.kind_of?(Array) ? value : record.ancestor_ids
-      return if ids.empty?
+      return if value.empty?
 
       if options[:integer]
-        unless ids.all? { |id| id.kind_of?(Integer) && id > 0 }
+        unless value.all? { |id| id.kind_of?(Integer) && id > 0 }
           record.errors.add(attribute, :invalid)
           return
         end
       end
 
-      if ids.include?(record.id)
+      if value.include?(record.id)
         record.errors.add(:base, I18n.t("ancestry.exclude_self", class_name: record.class.model_name.human))
       end
     end

lib/ancestry/has_ancestry.rb

@@ -127,12 +127,9 @@ def has_ancestry(options = {})
         attribute column, serializer, default: serializer.empty
       end
 
-      # ancestor_ids is the typed (array) view of the column
-      alias_attribute :ancestor_ids, column unless column == :ancestor_ids
-
       update_strategy = options[:update_strategy] || Ancestry.default_update_strategy
 
-      validates_with Ancestry::AncestryValidator, attributes: [column], integer: integer_pk
+      validates_with Ancestry::AncestryValidator, attributes: [:ancestor_ids], integer: integer_pk
 
       # Validate descendants' depths don't exceed max depth when moving them
       validate :ancestry_depth_of_descendants, if: :ancestry_changed?

lib/ancestry/instance_methods_builder.rb

@@ -62,11 +62,13 @@ def ancestor_ids
         end
 
         def ancestor_ids_in_database
-          attribute_in_database(:#{column})
+          value = attribute_in_database(:#{column})
+          value.kind_of?(Array) ? value : self.class.type_for_attribute("#{column}").deserialize(value)
         end
 
         def ancestor_ids_before_last_save
-          attribute_before_last_save(:#{column})
+          value = attribute_before_last_save(:#{column})
+          value.kind_of?(Array) ? value : self.class.type_for_attribute("#{column}").deserialize(value)
         end
 
         def parent_id_in_database
@@ -114,8 +116,8 @@ def sane_ancestor_ids?
           ids = ancestor_ids
           return true if ids.empty?
 
-          self.class.validators_on(:#{column}).each do |validator|
-            validator.validate_each(self, :#{column}, ids)
+          self.class.validators_on(:ancestor_ids).each do |validator|
+            validator.validate_each(self, :ancestor_ids, ids)
           end
           errors.none?
         ensure