Support Markdown rendering using multiple projectsrendering-markdown-multiple-projects

This refactors the Markdown pipeline so it supports the rendering of
multiple documents that may belong to different projects. An example of
where this happens is when displaying the event feed of a group. In this
case we retrieve events for all projects in the group. Previously we
would group events per project and render these chunks separately, but
this would result in many SQL queries being executed. By extending the
Markdown pipeline to support this out of the box we can drastically
reduce the number of SQL queries.

To achieve this we introduce a new object to the pipeline:
Banzai::RenderContext. This object simply wraps two other objects: an
optional Project instance, and an optional User instance. On its own
this wouldn't be very helpful, but a RenderContext can also be used to
associate HTML documents with specific Project instances. This work is
done in Banzai::ObjectRenderer and allows us to reuse as many queries
(and results) as possible.

1 files changed, 32 insertions, 0 deletions

diff --git a/lib/banzai/render_context.rb b/lib/banzai/render_context.rb
new file mode 100644
index 00000000000..e30fc9f469b
--- /dev/null
+++ b/lib/banzai/render_context.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module Banzai
+  # Object storing the current user, project, and other details used when
+  # parsing Markdown references.
+  class RenderContext
+    attr_reader :current_user
+
+    # default_project - The default project to use for all documents, if any.
+    # current_user - The user viewing the document, if any.
+    def initialize(default_project = nil, current_user = nil)
+      @current_user = current_user
+      @projects = Hash.new(default_project)
+    end
+
+    # Associates an HTML document with a Project.
+    #
+    # document - The HTML document to map to a Project.
+    # object - The object that produced the HTML document.
+    def associate_document(document, object)
+      # XML nodes respond to "document" but will return a Document instance,
+      # even when they belong to a DocumentFragment.
+      document = document.document if document.fragment?
+
+      @projects[document] = object.project if object.respond_to?(:project)
+    end
+
+    def project_for_node(node)
+      @projects[node.document]
+    end
+  end
+end