Debug exists subquery

lib/cancan.rb

@@ -24,4 +24,5 @@
   require 'cancan/model_adapters/strategies/base'
   require 'cancan/model_adapters/strategies/left_join'
   require 'cancan/model_adapters/strategies/subquery'
+  require 'cancan/model_adapters/strategies/exists_subquery'
 end

lib/cancan/model_adapters/strategies/exists_subquery.rb

@@ -0,0 +1,22 @@
+module CanCan
+  module ModelAdapters
+    class Strategies
+      class ExistsSubquery < Base
+        def execute!
+          model_class.where(joined_alias_exists_subquery_inner_query.arel.exists)
+        end
+
+        def joined_alias_exists_subquery_inner_query
+          model_class
+            .select('1')
+            .left_joins(joins)
+            .where(*where_conditions)
+            .where(
+              "#{quoted_table_name}.#{quoted_primary_key} = " \
+              "#{quoted_aliased_table_name}.#{quoted_primary_key}"
+            )
+        end
+      end
+    end
+  end
+end

spec/cancan/model_adapters/accessible_by_has_many_through_spec.rb

@@ -89,7 +89,8 @@ class Editor < ActiveRecord::Base
       if CanCan::ModelAdapters::ActiveRecordAdapter.version_greater_or_equal?('5.0.0')
         describe 'selecting custom columns' do
           it 'extracts custom columns correctly' do
-            posts = Post.accessible_by(ability).where(published: true).select('title as mytitle')
+            posts = Post.where(title: 'a').accessible_by(ability).where(published: true).select('title as mytitle')
+            puts posts.to_sql
             expect(posts[0].mytitle).to eq 'post1'
           end
         end