Get create activity from created object id.

This is useful for Ostatus federation because ostatus doesn't have
different ids for objects and activities...

lib/pleroma/activity.ex

@@ -18,4 +18,9 @@ defmodule Pleroma.Activity do
     Repo.all(from activity in Activity,
       where: fragment("? @> ?", activity.data, ^%{object: %{id: ap_id}}))
   end
+
+  def get_create_activity_by_object_ap_id(ap_id) do
+    Repo.one(from activity in Activity,
+      where: fragment("? @> ?", activity.data, ^%{type: "Create", object: %{id: ap_id}}))
+  end
 end

test/activity_test.exs

@@ -15,4 +15,11 @@ defmodule Pleroma.ActivityTest do
 
     assert activity == found_activity
   end
+
+  test "returns the activity that created an object" do
+    activity = insert(:note_activity)
+    found_activity = Pleroma.Activity.get_create_activity_by_object_ap_id(activity.data["object"]["id"])
+
+    assert activity == found_activity
+  end
 end

test/web/ostatus/feed_representer_test.exs

@@ -22,7 +22,7 @@ defmodule Pleroma.Web.OStatus.FeedRepresenterTest do
     |> :xmerl.export_simple_content(:xmerl_xml)
 
     expected = """
-    <feed xmlns="http://www.w3.org/2005/Atom" xmlns:activity="http://activitystrea.ms/spec/1.0/" xmlns:poco="http://portablecontacts.net/spec/1.0" xmlns:ostatus="http://ostatus.org/schema/1.0">
+    <feed xmlns="http://www.w3.org/2005/Atom" xmlns:thr="http://purl.org/syndication/thread/1.0" xmlns:activity="http://activitystrea.ms/spec/1.0/" xmlns:poco="http://portablecontacts.net/spec/1.0" xmlns:ostatus="http://ostatus.org/schema/1.0">
       <id>#{OStatus.feed_path(user)}</id>
       <title>#{user.nickname}'s timeline</title>
       <updated>#{most_recent_update}</updated>