From 223082e588af59cb35108ce2a2d742dcecf72cc6 Mon Sep 17 00:00:00 2001
From: Aaron Patterson <aaron.patterson@gmail.com>
Date: Thu, 10 Oct 2013 14:46:15 -0700
Subject: merge JoinDependency as outer joins

Merge JoinDependency objects as outer joins
---
 .../active_record/associations/join_dependency.rb  | 30 ++++++++++++++++++++++
 .../lib/active_record/relation/query_methods.rb    |  2 +-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/activerecord/lib/active_record/associations/join_dependency.rb b/activerecord/lib/active_record/associations/join_dependency.rb
index bc235cf63d..a25a061fc0 100644
--- a/activerecord/lib/active_record/associations/join_dependency.rb
+++ b/activerecord/lib/active_record/associations/join_dependency.rb
@@ -85,6 +85,20 @@ module ActiveRecord
         nodes
       end
 
+      def merge_outer_joins!(other)
+        left  = join_root
+        right = other.join_root
+
+        if left.match? right
+          merge_node left, right
+        else
+          # If the roots aren't the same, then deep copy the RHS to the LHS
+          left.children.concat right.children.map { |node|
+            deep_copy left, node
+          }
+        end
+      end
+
       def join_constraints
         join_root.flat_map(&:join_constraints)
       end
@@ -118,6 +132,22 @@ module ActiveRecord
 
       private
 
+      def merge_node(left, right)
+        intersection, missing = right.children.map { |node1|
+          [left.children.find { |node2| node1.match? node2 }, node1]
+        }.partition(&:first)
+
+        intersection.each { |l,r| merge_node l, r }
+
+        left.children.concat missing.map { |_,node| deep_copy left, node }
+      end
+
+      def deep_copy(parent, node)
+        dup = build_join_association(node.reflection, parent, Arel::OuterJoin)
+        dup.children.concat node.children.map { |n| deep_copy dup, n }
+        dup
+      end
+
       def find_node(target_node)
         stack = target_node.parents << target_node
 
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 364c7ec418..9c9690215a 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -951,7 +951,7 @@ module ActiveRecord
       )
 
       stashed_association_joins.each do |dep|
-        join_dependency.graft dep.outer_joins
+        join_dependency.merge_outer_joins! dep
       end
 
       joins = join_dependency.join_constraints
-- 
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