Speed up collection rendering and support collection caching

lib/jbuilder/collection_renderer.rb

@@ -0,0 +1,117 @@
+require 'delegate'
+
+begin
+  require 'action_view/renderer/collection_renderer'
+rescue LoadError
+  require 'action_view/renderer/partial_renderer'
+end
+
+class Jbuilder
+  module CollectionRenderable
+    extend ActiveSupport::Concern
+
+    class_methods do
+      def supports_collection_rendering?
+        superclass.private_method_defined?(:build_rendered_template) && superclass.private_method_defined?(:build_rendered_collection)
+      end
+    end
+
+    private
+
+    def build_rendered_template(content, template, layout = nil)
+      super(content || json.attributes!, template)
+    end
+
+    def build_rendered_collection(templates, _spacer)
+      json.merge!(templates.map(&:body))
+    end
+
+    def json
+      @options[:locals].fetch(:json)
+    end
+
+    class ScopedIterator < ::SimpleDelegator # :nodoc:
+      include Enumerable
+
+      def initialize(obj, scope)
+        super(obj)
+        @scope = scope
+      end
+
+      # Rails 6.0 support:
+      def each
+        return enum_for(:each) unless block_given?
+
+        __getobj__.each do |object|
+          @scope.call { yield(object) }
+        end
+      end
+
+      # Rails 6.1 support:
+      def each_with_info
+        return enum_for(:each_with_info) unless block_given?
+
+        __getobj__.each_with_info do |object, (path, as, counter, iteration)|
+          @scope.call { yield(object, [path, as, counter, iteration]) }
+        end
+      end
+    end
+
+    private_constant :ScopedIterator
+  end
+
+  collection_renderer_available = begin
+                                     ::ActionView::CollectionRenderer
+
+                                     true
+                                   rescue ::NameError
+                                     false
+                                   end
+
+  if collection_renderer_available
+    # Rails 6.1 support:
+    class CollectionRenderer < ::ActionView::CollectionRenderer
+      include CollectionRenderable
+
+      def initialize(lookup_context, options, &scope)
+        super(lookup_context, options)
+        @scope = scope
+      end
+
+      private
+
+        def collection_with_template(view, template, layout, collection)
+          super(view, template, layout, ScopedIterator.new(collection, @scope))
+        end
+    end
+  else
+    # Rails 6.0 support:
+    class CollectionRenderer < ::ActionView::PartialRenderer
+      include CollectionRenderable
+
+      def initialize(lookup_context, options, &scope)
+        super(lookup_context)
+        @options = options
+        @scope = scope
+      end
+
+      def render_collection_with_partial(collection, partial, context, block)
+        render(context, @options.merge(collection: collection, partial: partial), block)
+      end
+
+      private
+
+        def collection_without_template(view)
+          @collection = ScopedIterator.new(@collection, @scope)
+
+          super(view)
+        end
+
+        def collection_with_template(view, template)
+          @collection = ScopedIterator.new(@collection, @scope)
+
+          super(view, template)
+        end
+    end
+  end
+end

lib/jbuilder/jbuilder_template.rb

@@ -1,4 +1,5 @@
 require 'jbuilder/jbuilder'
+require 'jbuilder/collection_renderer'
 require 'action_dispatch/http/mime_type'
 require 'active_support/cache'
 
@@ -104,11 +105,30 @@ def set!(name, object = BLANK, *args)
   private
 
   def _render_partial_with_options(options)
-    options.reverse_merge! locals: options.except(:partial, :as, :collection)
+    options.reverse_merge! locals: options.except(:partial, :as, :collection, :cached)
     options.reverse_merge! ::JbuilderTemplate.template_lookup_options
     as = options[:as]
 
-    if as && options.key?(:collection)
+    if options.key?(:collection) && options[:collection].nil?
+      array!
+    elsif as && options.key?(:collection) && CollectionRenderer.supports_collection_rendering?
+      collection = options.delete(:collection) || []
+      partial = options.delete(:partial)
+      options[:locals].merge!(json: self)
+
+      if options.has_key?(:layout)
+        raise ::NotImplementedError, "The `:layout' option is not supported in collection rendering."
+      end
+
+      if options.has_key?(:spacer_template)
+        raise ::NotImplementedError, "The `:spacer_template' option is not supported in collection rendering."
+      end
+
+      CollectionRenderer
+        .new(@context.lookup_context, options) { |&block| _scope(&block) }
+        .render_collection_with_partial(collection, partial, @context, nil)
+    elsif as && options.key?(:collection) && !CollectionRenderer.supports_collection_rendering?
+      # For Rails <= 5.2:
       as = as.to_sym
       collection = options.delete(:collection)
       locals = options.delete(:locals)

test/jbuilder_template_test.rb

@@ -283,6 +283,51 @@ class JbuilderTemplateTest < ActiveSupport::TestCase
     assert_equal "David", result["firstName"]
   end
 
+  if JbuilderTemplate::CollectionRenderer.supports_collection_rendering?
+    test "supports the cached: true option" do
+      result = render('json.array! @posts, partial: "post", as: :post, cached: true', posts: POSTS)
+
+      assert_equal 10, result.count
+      assert_equal "Post #5", result[4]["body"]
+      assert_equal "Heinemeier Hansson", result[2]["author"]["last_name"]
+      assert_equal "Pavel", result[5]["author"]["first_name"]
+
+      expected = {
+        "id" => 1,
+        "body" => "Post #1",
+        "author" => {
+          "first_name" => "David",
+          "last_name" => "Heinemeier Hansson"
+        }
+      }
+
+      assert_equal expected, Rails.cache.read("post-1")
+
+      result = render('json.array! @posts, partial: "post", as: :post, cached: true', posts: POSTS)
+
+      assert_equal 10, result.count
+      assert_equal "Post #5", result[4]["body"]
+      assert_equal "Heinemeier Hansson", result[2]["author"]["last_name"]
+      assert_equal "Pavel", result[5]["author"]["first_name"]
+    end
+
+    test "raises an error on a render call with the :layout option" do
+      error = assert_raises NotImplementedError do
+        render('json.array! @posts, partial: "post", as: :post, layout: "layout"', posts: POSTS)
+      end
+
+      assert_equal "The `:layout' option is not supported in collection rendering.", error.message
+    end
+
+    test "raises an error on a render call with the :spacer_template option" do
+      error = assert_raises NotImplementedError do
+        render('json.array! @posts, partial: "post", as: :post, spacer_template: "template"', posts: POSTS)
+      end
+
+      assert_equal "The `:spacer_template' option is not supported in collection rendering.", error.message
+    end
+  end
+
   private
     def render(*args)
       JSON.load render_without_parsing(*args)
@@ -305,7 +350,21 @@ def build_view(options = {})
         ActionView::Base.new(lookup_context, options.fetch(:assigns, {}), controller)
       end
 
-      def view.view_cache_dependencies; []; end
+      def view.view_cache_dependencies
+        []
+      end
+
+      def view.combined_fragment_cache_key(key)
+        [ key ]
+      end
+
+      def view.cache_fragment_name(key, *)
+        key
+      end
+
+      def view.fragment_name_with_digest(key)
+        key
+      end
 
       view
     end

test/test_helper.rb

@@ -21,14 +21,19 @@ def cache
   end
 end
 
-class Post < Struct.new(:id, :body, :author_name); end
+if JbuilderTemplate::CollectionRenderer.supports_collection_rendering?
+  Jbuilder::CollectionRenderer.collection_cache = Rails.cache
+end
+
+class Post < Struct.new(:id, :body, :author_name)
+  def cache_key
+    "post-#{id}"
+  end
+end
 
 class Racer < Struct.new(:id, :name)
   extend ActiveModel::Naming
   include ActiveModel::Conversion
 end
 
 ActionView::Template.register_template_handler :jbuilder, JbuilderHandler
-
-ActionView::Base.remove_possible_method :fragment_name_with_digest
-ActionView::Base.remove_possible_method :cache_fragment_name