From d1e0f11b49c9c7598efffbc44a94539b6e982e5c Mon Sep 17 00:00:00 2001
From: Ryuta Kamizono <kamipo@gmail.com>
Date: Mon, 18 Jul 2016 22:11:35 +0900
Subject: Delegate to `scope` rather than `merge!` for collection proxy

`merge! association.scope(nullify: false)` is expensive but most methods
do not need the merge.
---
 .../associations/collection_association.rb         |  6 ++--
 .../active_record/associations/collection_proxy.rb | 32 ++++++++++++++--------
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 46923f690a..f747491a12 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -313,9 +313,9 @@ module ActiveRecord
         record
       end
 
-      def scope(opts = {})
-        scope = super()
-        scope.none! if opts.fetch(:nullify, true) && null_scope?
+      def scope
+        scope = super
+        scope.none! if null_scope?
         scope
       end
 
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index 9f91f2b536..63f746688c 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -28,12 +28,9 @@ module ActiveRecord
     # is computed directly through SQL and does not trigger by itself the
     # instantiation of the actual post records.
     class CollectionProxy < Relation
-      delegate :exists?, :update_all, :arel, to: :scope
-
       def initialize(klass, association) #:nodoc:
         @association = association
         super klass, klass.arel_table, klass.predicate_builder
-        merge! association.scope(nullify: false)
       end
 
       def target
@@ -956,14 +953,6 @@ module ActiveRecord
         @association
       end
 
-      # We don't want this object to be put on the scoping stack, because
-      # that could create an infinite loop where we call an @association
-      # method, which gets the current scope, which is this object, which
-      # delegates to @association, and so on.
-      def scoping
-        @association.scope.scoping { yield }
-      end
-
       # Returns a <tt>Relation</tt> object for the records in this association
       def scope
         @association.scope
@@ -1126,6 +1115,19 @@ module ActiveRecord
         self
       end
 
+      def respond_to?(name, include_private = false)
+        super || scope.respond_to?(name, include_private)
+      end
+
+      delegate_methods = [
+        QueryMethods,
+        SpawnMethods,
+      ].flat_map { |klass|
+        klass.public_instance_methods(false)
+      } - self.public_instance_methods(false) + [:scoping]
+
+      delegate(*delegate_methods, to: :scope)
+
       private
 
         def find_nth_with_limit(index, limit) # :doc:
@@ -1149,6 +1151,14 @@ module ActiveRecord
         def exec_queries
           load_target
         end
+
+        def method_missing(method, *args, &block)
+          if scope.respond_to?(method)
+            scope.public_send(method, *args, &block)
+          else
+            super
+          end
+        end
     end
   end
 end
-- 
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