Cache root (#370)

Add cache_root! for faster root caching

lib/jbuilder/jbuilder_template.rb

@@ -42,6 +42,27 @@ def cache!(key=nil, options={})
     end
   end
 
+  # Caches the json structure at the root using a string rather than the hash structure. This is considerably
+  # faster, but the drawback is that it only works, as the name hints, at the root. So you cannot
+  # use this approach to cache deeper inside the hierarchy, like in partials or such. Continue to use #cache! there.
+  #
+  # Example:
+  #
+  #   json.cache_root! @person do
+  #     json.extract! @person, :name, :age
+  #   end
+  #
+  #   # json.extra 'This will not work either, the root must be exclusive'
+  def cache_root!(key=nil, options={})
+    if @context.controller.perform_caching
+      raise "cache_root! can't be used after JSON structures have been defined" if @attributes.present?
+
+      @cached_root = _cache_fragment_for([ :root, key ], options) { yield; target! }
+    else
+      yield
+    end
+  end
+
   # Conditionally caches the json depending in the condition given as first parameter. Has the same
   # signature as the `cache` helper method in `ActionView::Helpers::CacheHelper` and so can be used in
   # the same way.
@@ -55,6 +76,10 @@ def cache_if!(condition, *args)
     condition ? cache!(*args, &::Proc.new) : yield
   end
 
+  def target!
+    @cached_root || super
+  end
+
   def array!(collection = [], *args)
     options = args.first
 

test/jbuilder_template_test.rb

@@ -386,6 +386,35 @@ def assert_collection_rendered(result, context = nil)
     JBUILDER
   end
 
+  test "caching root structure" do
+    undef_context_methods :fragment_name_with_digest, :cache_fragment_name
+
+    cache_miss_result = jbuild <<-JBUILDER
+      json.cache_root! "cachekey" do
+        json.name "Miss"
+      end
+    JBUILDER
+
+    cache_hit_result = jbuild <<-JBUILDER
+      json.cache_root! "cachekey" do
+        json.name "Hit"
+      end
+    JBUILDER
+
+    assert_equal cache_miss_result, cache_hit_result
+  end
+
+  test "failing to cache root after attributes have been defined" do
+    assert_raises ActionView::Template::Error, "cache_root! can't be used after JSON structures have been defined" do
+      jbuild <<-JBUILDER
+        json.name "Kaboom"
+        json.cache_root! "cachekey" do
+          json.name "Miss"
+        end
+      JBUILDER
+    end
+  end
+
   test "does not perform caching when controller.perform_caching is false" do
     controller.perform_caching = false