Merge pull request rails#6521 from Empact/throw-result

Fix that #exists? can blow up with ThrowResult exception

Author: rafaelfranca

activerecord/lib/active_record/relation/finder_methods.rb

@@ -186,6 +186,8 @@ def exists?(id = false)
       end
 
       connection.select_value(relation, "#{name} Exists", relation.bind_values)
+    rescue ThrowResult
+      false
     end
 
     protected

activerecord/test/cases/finder_test.rb

@@ -69,7 +69,12 @@ def test_exists_with_order
     assert Topic.order(:id).uniq.exists?
   end
 
-  def test_does_not_exist_with_empty_table_and_no_args_given
+  def test_exists_with_includes_limit_and_empty_result
+    assert !Topic.includes(:replies).limit(0).exists?
+    assert !Topic.includes(:replies).limit(1).where('0 = 1').exists?
+  end
+
+  def test_exists_with_empty_table_and_no_args_given
     Topic.delete_all
     assert !Topic.exists?
   end