searchable: fixup bugs in e7b454686.

app/logical/concerns/searchable.rb

@@ -35,7 +35,7 @@ module Searchable
     elsif has_attribute?(field)
       node = arel_table[field]
     else
-      node = Arel.sql(field)
+      node = Arel.sql(field.to_s)
     end
 
     arel = node.send(operator, *args, **options)

app/models/post.rb

@@ -658,12 +658,12 @@ class Post < ApplicationRecord
           end
 
         when /^-child:(.+)$/i
-          children.numeric_attribute_matches(:id, $1).each do |post|
+          children.search(id: $1).each do |post|
             post.update!(parent_id: nil)
           end
 
         when /^child:(.+)$/i
-          Post.numeric_attribute_matches(:id, $1).where.not(id: id).limit(10).each do |post|
+          Post.search(id: $1).where.not(id: id).limit(10).each do |post|
             post.update!(parent_id: id)
           end