swap out some n^2 for some n

1 files changed, 13 insertions, 7 deletions

diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index e644670019..b8b0898cc8 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -26,15 +26,21 @@ module ActiveRecord
 
       merged_relation = merged_relation.joins(r.joins_values)
 
-      merged_wheres = @where_values.dup
+      merged_wheres = @where_values.dup + r.where_values
 
-      r.where_values.each do |w|
-        if w.respond_to?(:operator) && w.operator == :==
-          merged_wheres = merged_wheres.reject {|p| p.respond_to?(:operator) && p.operator == :== && p.operand1.name == w.operand1.name }
-        end
+      equality_wheres = merged_wheres.find_all { |w|
+        w.respond_to?(:operator) && w.operator == :==
+      }
 
-        merged_wheres << w
-      end
+      equality_wheres_by_operand = equality_wheres.group_by { |eq|
+        eq.left.name
+      }
+
+      duplicates = equality_wheres_by_operand.map { |name, list|
+        list[0...-1]
+      }.flatten
+
+      merged_wheres -= duplicates
 
       merged_relation.where_values = merged_wheres