ObjectView: do not fetch an object for its ID

Non-Create/Listen activities had their associated object field
normalized and fetched, but only to use their `id` field, which is both
slow and redundant. This also failed on Undo activities, which delete
the associated object/activity in database.

Undo activities will now render properly and database loads should
improve ever so slightly.

2 files changed, 12 insertions, 7 deletions

diff --git a/lib/pleroma/object.ex b/lib/pleroma/object.ex
index fee3f1842..38accae5d 100644
--- a/lib/pleroma/object.ex
+++ b/lib/pleroma/object.ex
@@ -144,7 +144,7 @@ defmodule Pleroma.Object do
     Logger.debug("Backtrace: #{inspect(Process.info(:erlang.self(), :current_stacktrace))}")
   end
 
-  def normalize(_, options \\ [fetch: false])
+  def normalize(_, options \\ [fetch: false, id_only: false])
 
   # If we pass an Activity to Object.normalize(), we can try to use the preloaded object.
   # Use this whenever possible, especially when walking graphs in an O(N) loop!
@@ -172,10 +172,15 @@ defmodule Pleroma.Object do
   def normalize(%{"id" => ap_id}, options), do: normalize(ap_id, options)
 
   def normalize(ap_id, options) when is_binary(ap_id) do
-    if Keyword.get(options, :fetch) do
-      Fetcher.fetch_object_from_id!(ap_id, options)
-    else
-      get_cached_by_ap_id(ap_id)
+    cond do
+      Keyword.get(options, :id_only) ->
+        ap_id
+
+      Keyword.get(options, :fetch) ->
+        Fetcher.fetch_object_from_id!(ap_id, options)
+
+      true ->
+        get_cached_by_ap_id(ap_id)
     end
   end
 
diff --git a/lib/pleroma/web/activity_pub/views/object_view.ex b/lib/pleroma/web/activity_pub/views/object_view.ex
index f848aba3a..63caa915c 100644
--- a/lib/pleroma/web/activity_pub/views/object_view.ex
+++ b/lib/pleroma/web/activity_pub/views/object_view.ex
@@ -29,11 +29,11 @@ defmodule Pleroma.Web.ActivityPub.ObjectView do
 
   def render("object.json", %{object: %Activity{} = activity}) do
     base = Pleroma.Web.ActivityPub.Utils.make_json_ld_header()
-    object = Object.normalize(activity, fetch: false)
+    object_id = Object.normalize(activity, id_only: true)
 
     additional =
       Transmogrifier.prepare_object(activity.data)
-      |> Map.put("object", object.data["id"])
+      |> Map.put("object", object_id)
 
     Map.merge(base, additional)
   end