From 110e0e1fcceab68716e0c75d87baffb14403b288 Mon Sep 17 00:00:00 2001
From: Maxime Lapointe <hunter_spawn@hotmail.com>
Date: Tue, 25 Jul 2017 14:00:39 -0400
Subject: Avoid duplicate clauses when using #or Condenses the clauses that are
 common to both sides of the OR and put them outside, before the OR This fix
 the current behavior where the number of conditions is exponential based on
 the number of times #or is used.

---
 .../lib/active_record/relation/where_clause.rb     | 25 ++++++++++++++--------
 1 file changed, 16 insertions(+), 9 deletions(-)

(limited to 'activerecord/lib/active_record/relation/where_clause.rb')

diff --git a/activerecord/lib/active_record/relation/where_clause.rb b/activerecord/lib/active_record/relation/where_clause.rb
index ef2bca9155..5b68c25bdd 100644
--- a/activerecord/lib/active_record/relation/where_clause.rb
+++ b/activerecord/lib/active_record/relation/where_clause.rb
@@ -15,6 +15,12 @@ module ActiveRecord
         )
       end
 
+      def -(other)
+        WhereClause.new(
+          predicates - other.predicates,
+        )
+      end
+
       def merge(other)
         WhereClause.new(
           predicates_unreferenced_by(other) + other.predicates,
@@ -26,15 +32,16 @@ module ActiveRecord
       end
 
       def or(other)
-        if empty?
-          self
-        elsif other.empty?
-          other
-        else
-          WhereClause.new(
-            [ast.or(other.ast)],
-          )
-        end
+        left = self - other
+        common = self - left
+        right = other - common
+
+        return common if left.empty? || right.empty?
+
+        or_clause = WhereClause.new(
+          [left.ast.or(right.ast)]
+        )
+        common + or_clause
       end
 
       def to_h(table_name = nil)
-- 
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