Optimize ActiveRecord::Relation#exists? with no conditions for loaded relations

Author: fatkodima

activerecord/lib/active_record/relation/finder_methods.rb

@@ -365,6 +365,7 @@ def exists?(conditions = :none)
       end
 
       return false if !conditions || limit_value == 0
+      return !records.empty? if conditions == :none && loaded?
 
       if eager_loading?
         relation = apply_join_dependency(eager_loading: false)

activerecord/test/cases/finder_test.rb

@@ -285,6 +285,19 @@ def test_exists_returns_true_with_one_record_and_no_args
     assert_equal true, Topic.exists?
   end
 
+  def test_exists_with_loaded_relation
+    topics = Topic.all.load
+    assert_no_queries do
+      assert_equal true, topics.exists?
+    end
+
+    Topic.delete_all
+    topics = Topic.all.load
+    assert_no_queries do
+      assert_equal false, topics.exists?
+    end
+  end
+
   def test_exists_returns_false_with_false_arg
     assert_equal false, Topic.exists?(false)
   end