From c09829e03db611b46bb52e2054991222cf57bfbe Mon Sep 17 00:00:00 2001
From: Andrew Horner <andrew@tablexi.com>
Date: Thu, 18 Apr 2013 23:41:58 -0500
Subject: Preserve context for joins while merging relations

This is a backport of #10164, already merged into
master. The issue is described in lengthy detail
in issues #3002 and #5494.
---
 .../active_record/associations/join_dependency.rb  |  2 +-
 .../join_dependency/join_association.rb            |  7 +++++-
 .../lib/active_record/relation/spawn_methods.rb    | 28 +++++++++++++++++++++-
 3 files changed, 34 insertions(+), 3 deletions(-)

(limited to 'activerecord/lib/active_record')

diff --git a/activerecord/lib/active_record/associations/join_dependency.rb b/activerecord/lib/active_record/associations/join_dependency.rb
index cd366ac8b7..e3d8356f49 100644
--- a/activerecord/lib/active_record/associations/join_dependency.rb
+++ b/activerecord/lib/active_record/associations/join_dependency.rb
@@ -109,7 +109,7 @@ module ActiveRecord
         case associations
         when Symbol, String
           reflection = parent.reflections[associations.to_s.intern] or
-          raise ConfigurationError, "Association named '#{ associations }' was not found; perhaps you misspelled it?"
+          raise ConfigurationError, "Association named '#{ associations }' was not found on #{parent.active_record.name}; perhaps you misspelled it?"
           unless join_association = find_join_association(reflection, parent)
             @reflections << reflection
             join_association = build_join_association(reflection, parent)
diff --git a/activerecord/lib/active_record/associations/join_dependency/join_association.rb b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
index 03963ab060..becf1a3f62 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_association.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
@@ -55,7 +55,12 @@ module ActiveRecord
 
         def find_parent_in(other_join_dependency)
           other_join_dependency.join_parts.detect do |join_part|
-            parent == join_part
+            case parent
+            when JoinBase
+              parent.active_record == join_part.active_record
+            else
+              parent == join_part
+            end
           end
         end
 
diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index b8e384c2f3..90f2ac3cde 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -27,7 +27,7 @@ module ActiveRecord
         merge_relation_method(merged_relation, method, value) if value.present?
       end
 
-      merged_relation.joins_values += r.joins_values
+      merge_joins(merged_relation, r)
 
       merged_wheres = @where_values + r.where_values
 
@@ -146,6 +146,32 @@ module ActiveRecord
 
     private
 
+      def merge_joins(relation, other)
+        values = other.joins_values
+        return if values.blank?
+
+        if other.klass == relation.klass
+          relation.joins_values += values
+        else
+          joins_dependency, rest = values.partition do |join|
+            case join
+            when Hash, Symbol, Array
+              true
+            else
+              false
+            end
+          end
+
+          join_dependency = ActiveRecord::Associations::JoinDependency.new(
+            other.klass,
+            joins_dependency,
+            []
+          )
+
+          relation.joins_values += join_dependency.join_associations + rest
+        end
+      end
+
       def merge_relation_method(relation, method, value)
         relation.send(:"#{method}_values=", relation.send(:"#{method}_values") + value)
       end
-- 
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