object: add support for preloading objects when walking an activity graph in normal form

lib/pleroma/activity.ex

@@ -7,6 +7,7 @@ defmodule Pleroma.Activity do
 
   alias Pleroma.Activity
   alias Pleroma.Notification
+  alias Pleroma.Object
   alias Pleroma.Repo
 
   import Ecto.Query
@@ -33,6 +34,18 @@ defmodule Pleroma.Activity do
     field(:recipients, {:array, :string})
     has_many(:notifications, Notification, on_delete: :delete_all)
 
+    # Attention: this is a fake relation, don't try to preload it blindly and expect it to work!
+    # The foreign key is embedded in a jsonb field.
+    #
+    # To use it, you probably want to do an inner join and a preload:
+    #
+    # ```
+    # |> join(:inner, [activity], o in Object,
+    #    fragment("(?->>'id') = COALESCE((? -> 'object'::text) ->> 'id'::text)", o.data, activity.data))
+    # |> preload([activity, object], [object: object])
+    # ```
+    has_one(:object, Object, on_delete: :nothing, foreign_key: :id)
+
     timestamps()
   end
 
@@ -49,6 +62,21 @@ defmodule Pleroma.Activity do
     Repo.get(Activity, id)
   end
 
+  def get_by_id_with_object(id) do
+    from(activity in Activity,
+      where: activity.id == ^id,
+      inner_join: o in Object,
+      on:
+        fragment(
+          "(?->>'id') = COALESCE((? -> 'object'::text) ->> 'id'::text)",
+          o.data,
+          activity.data
+        ),
+      preload: [object: o]
+    )
+    |> Repo.one()
+  end
+
   def by_object_ap_id(ap_id) do
     from(
       activity in Activity,
@@ -76,7 +104,7 @@ defmodule Pleroma.Activity do
     )
   end
 
-  def create_by_object_ap_id(ap_id) do
+  def create_by_object_ap_id(ap_id) when is_binary(ap_id) do
     from(
       activity in Activity,
       where:
@@ -90,6 +118,8 @@ defmodule Pleroma.Activity do
     )
   end
 
+  def create_by_object_ap_id(_), do: nil
+
   def get_all_create_by_object_ap_id(ap_id) do
     Repo.all(create_by_object_ap_id(ap_id))
   end
@@ -101,6 +131,36 @@ defmodule Pleroma.Activity do
 
   def get_create_by_object_ap_id(_), do: nil
 
+  def create_by_object_ap_id_with_object(ap_id) when is_binary(ap_id) do
+    from(
+      activity in Activity,
+      where:
+        fragment(
+          "coalesce((?)->'object'->>'id', (?)->>'object') = ?",
+          activity.data,
+          activity.data,
+          ^to_string(ap_id)
+        ),
+      where: fragment("(?)->>'type' = 'Create'", activity.data),
+      inner_join: o in Object,
+      on:
+        fragment(
+          "(?->>'id') = COALESCE((? -> 'object'::text) ->> 'id'::text)",
+          o.data,
+          activity.data
+        ),
+      preload: [object: o]
+    )
+  end
+
+  def create_by_object_ap_id_with_object(_), do: nil
+
+  def get_create_by_object_ap_id_with_object(ap_id) do
+    ap_id
+    |> create_by_object_ap_id_with_object()
+    |> Repo.one()
+  end
+
   def normalize(obj) when is_map(obj), do: Activity.get_by_ap_id(obj["id"])
   def normalize(ap_id) when is_binary(ap_id), do: Activity.get_by_ap_id(ap_id)
   def normalize(_), do: nil