Add recipients field to activities.

Also do some very basic checks for AP message insertion.

priv/repo/migrations/20171212163643_add_recipients_to_activities.exs

@@ -0,0 +1,11 @@
+defmodule Pleroma.Repo.Migrations.AddRecipientsToActivities do
+  use Ecto.Migration
+
+  def change do
+    alter table(:activities) do
+      add :recipients, {:array, :string}
+    end
+
+    create index(:activities, [:recipients], using: :gin)
+  end
+end

priv/repo/migrations/20171212164525_fill_recipients_in_activities.exs

@@ -0,0 +1,21 @@
+defmodule Pleroma.Repo.Migrations.FillRecipientsInActivities do
+  use Ecto.Migration
+  alias Pleroma.{Repo, Activity}
+
+  def up do
+    max = Repo.aggregate(Activity, :max, :id)
+    if max do
+      IO.puts("#{max} activities")
+      chunks = 0..(round(max / 10_000))
+
+      Enum.each(chunks, fn (i) ->
+        min = i * 10_000
+        max = min + 10_000
+        execute("""
+        update activities set recipients = array(select jsonb_array_elements_text(data->'to')) where id > #{min} and id <= #{max};
+        """)
+        |> IO.inspect
+      end)
+    end
+  end
+end