Allow scopes that define string SQL joins

lib/ransack/adapters/active_record/context.rb

@@ -139,6 +139,7 @@ module Ransack
             stashed.eql?(association)
           }
           @object.joins_values.delete_if { |jd|
+            jd.instance_variables.include?(:@join_root) &&
             jd.instance_variable_get(:@join_root).children.map(&:object_id) == [association.object_id]
           }
         end

spec/ransack/adapters/active_record/base_spec.rb

@@ -78,6 +78,16 @@ module Ransack
               expect(s.result.to_sql).to (include 'active = 1')
             end
 
+            it 'applies scopes that define string SQL joins' do
+              allow(Article)
+                .to receive(:ransackable_scopes)
+                .and_return([:latest_comment_cont])
+
+              # Including a negative condition to test removing the scope
+              s = Search.new(Article, notes_note_not_eq: 'Test', latest_comment_cont: 'Test')
+              expect(s.result.to_sql).to include 'latest_comment'
+            end
+
             context "with sanitize_custom_scope_booleans set to false" do
               before(:all) do
                 Ransack.configure { |c| c.sanitize_custom_scope_booleans = false }

spec/support/schema.rb

@@ -138,6 +138,22 @@ class Article < ActiveRecord::Base
   alias_attribute :content, :body
 
   default_scope { where("'default_scope' = 'default_scope'") }
+  scope :latest_comment_cont, lambda { |msg|
+    join = <<-SQL
+      (LEFT OUTER JOIN (
+          SELECT
+            comments.*,
+            row_number() OVER (PARTITION BY comments.article_id ORDER BY comments.id DESC) AS rownum
+          FROM comments
+        ) AS latest_comment
+        ON latest_comment.article_id = article.id
+        AND latest_comment.rownum = 1
+      )
+    SQL
+    .squish
+
+    joins(join).where("latest_comment.body ILIKE ?", "%#{msg}%")
+  }
 end
 
 class StoryArticle < Article