Don't remove join dependencies in `Relation#exists?`

Fixes #18632

3 files changed, 13 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index cb3e27838b..63cd715920 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Don't remove join dependencies in `Relation#exists?`
+
+    Fixes #18632
+
+    *Sean Griffin*
+
 *   Invalid values assigned to a JSON column are assumed to be `nil`.
 
     Fixes #18629.
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 088bc203b7..c83abfba06 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -307,7 +307,7 @@ module ActiveRecord
         relation = relation.where(conditions)
       else
         unless conditions == :none
-          relation = where(primary_key => conditions)
+          relation = relation.where(primary_key => conditions)
         end
       end
 
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 9631ea79be..d272b9b929 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -857,6 +857,12 @@ class RelationTest < ActiveRecord::TestCase
     assert ! fake.exists?(authors(:david).id)
   end
 
+  def test_exists_uses_existing_scope
+    post = authors(:david).posts.first
+    authors = Author.includes(:posts).where(name: "David", posts: { id: post.id })
+    assert authors.exists?(authors(:david).id)
+  end
+
   def test_last
     authors = Author.all
     assert_equal authors(:bob), authors.last