Backport "Delegate to scope rather than merge! for collection proxy"

activerecord/lib/active_record/associations/association.rb

@@ -83,7 +83,7 @@ def target=(target)
       end
 
       def scope
-        target_scope.merge(association_scope)
+        target_scope.merge!(association_scope)
       end
 
       # The scope for this association.

activerecord/lib/active_record/associations/collection_association.rb

@@ -39,13 +39,7 @@ def reader(force_reload = false)
           reload
         end
 
-        if null_scope?
-          # Cache the proxy separately before the owner has an id
-          # or else a post-save proxy will still lack the id
-          @null_proxy ||= CollectionProxy.create(klass, self)
-        else
-          @proxy ||= CollectionProxy.create(klass, self)
-        end
+        CollectionProxy.create(klass, self)
       end
 
       # Implements the writer method, e.g. foo.items= for Foo.has_many :items
@@ -455,9 +449,9 @@ def replace_on_target(record, index, skip_callbacks)
         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
 

activerecord/lib/active_record/associations/collection_proxy.rb

@@ -28,12 +28,9 @@ module Associations
     # 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
@@ -902,19 +899,10 @@ def proxy_association
         @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
+        @scope ||= @association.scope
       end
-      alias spawn scope
 
       # Equivalent to <tt>Array#==</tt>. Returns +true+ if the two arrays
       # contain the same number of elements and if each element is equal
@@ -1046,6 +1034,7 @@ def clear
       #   person.pets(true)  # fetches pets from the database
       #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
       def reload
+        @scope = nil
         proxy_association.reload
         self
       end
@@ -1067,11 +1056,21 @@ def reload
       #   person.pets  # fetches pets from the database
       #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
       def reset
+        @scope = nil
         proxy_association.reset
         proxy_association.reset_scope
         self
       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 null_scope?
@@ -1081,6 +1080,18 @@ def null_scope?
         def exec_queries
           load_target
         end
+
+        def respond_to_missing?(method, _)
+          scope.respond_to?(method) || super
+        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

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -594,6 +594,17 @@ def test_update_all_on_association_accessed_before_save_with_explicit_foreign_ke
     firm.save!
     assert_equal firm.clients.count, firm.clients.update_all(description: 'Great!')
     assert_equal clients_proxy_id, firm.clients.object_id
+    firm = Firm.new(name: "Firm")
+    firm.clients << Client.first
+    firm.save!
+    assert_equal firm.clients.count, firm.clients.update_all(description: "Great!")
+  end
+
+  def test_update_all_on_association_accessed_before_save_with_explicit_foreign_key
+    firm = Firm.new(name: "Firm", id: 100)
+    firm.clients << Client.first
+    firm.save!
+    assert_equal firm.clients.count, firm.clients.update_all(description: "Great!")
   end
 
   def test_belongs_to_sanity

activerecord/test/cases/associations_test.rb

@@ -237,11 +237,6 @@ def test_scoped_allows_conditions
     assert_equal david.projects, david.projects.scope
   end
 
-  test "proxy object is cached" do
-    david = developers(:david)
-    assert david.projects.equal?(david.projects)
-  end
-
   test "inverses get set of subsets of the association" do
     man = Man.create
     man.interests.create