prune_objects can prune orphaned activities who reference an array of objects

E.g. Flag activities have an array of objects

We prune the activity when NONE of the objects can be found

Note that the cost of finding and deleting these is ~4x higher than finding and deleting the non-array ones

Only string:
Delete on activities  (cost=506573.48..506580.38 rows=0 width=0)

Only Array:
Delete on activities  (cost=3570359.68..4276365.34 rows=0 width=0)

(They are still executed separately, so the total cost is the sum of the two)

lib/mix/tasks/pleroma/database.ex

@@ -172,6 +172,7 @@ def run(["prune_objects" | args]) do
     |> Repo.delete_all(timeout: :infinity)
 
     if Keyword.get(options, :prune_orphaned_activities) do
+      # Prune activities who link to a single object
       """
       delete from public.activities
       where id in (
@@ -179,28 +180,40 @@ def run(["prune_objects" | args]) do
         left join public.objects o on a.data ->> 'object' = o.data ->> 'id'
         left join public.activities a2 on a.data ->> 'object' = a2.data ->> 'id'
         left join public.users u  on a.data ->> 'object' = u.ap_id
-      -- Only clean up remote activities
         where not a.local
-      -- For now we only focus on activities with direct links to objects
-      --     e.g. not json objects (in case of embedded objects) or json arrays (in case of multiple objects)
         and jsonb_typeof(a."data" -> 'object') = 'string'
-      -- Find Activities that don't have existing objects
         and o.id is null
         and a2.id is null
         and u.id is null
       )
       """
-      |> Repo.query()
+      |> Repo.query([], timeout: :infinity)
+
+      # Prune activities who link to an array of objects
+      """
+      delete from public.activities
+      where id in (
+        select a.id from public.activities a
+        join json_array_elements_text((a."data" -> 'object')::json) as j on jsonb_typeof(a."data" -> 'object') = 'array'
+        left join public.objects o on j.value = o.data ->> 'id'
+        left join public.activities a2 on j.value = a2.data ->> 'id'
+        left join public.users u  on j.value = u.ap_id
+        group by a.id
+        having max(o.data ->> 'id') is null
+        and max(a2.data ->> 'id') is null
+        and max(u.ap_id) is null
+      )
+      """
+      |> Repo.query([], timeout: :infinity)
     end
 
-    prune_hashtags_query = """
+    """
     DELETE FROM hashtags AS ht
     WHERE NOT EXISTS (
       SELECT 1 FROM hashtags_objects hto
       WHERE ht.id = hto.hashtag_id)
     """
-
-    Repo.query(prune_hashtags_query)
+    |> Repo.query()
 
     if Keyword.get(options, :vacuum) do
       Maintenance.vacuum("full")

test/mix/tasks/pleroma/database_test.exs

@@ -354,7 +354,7 @@ test "with the --keep-threads option it keeps old threads with bookmarked posts"
       assert length(Repo.all(Object)) == 1
     end
 
-    test "We don't have unexpected tables which can contain objects that are referenced by activities" do
+    test "We don't have unexpected tables which may contain objects that are referenced by activities" do
       # We can delete orphaned activities. For that we look for the objects they reference in the 'objects', 'activities', and 'users' table.
       # If someone adds another table with objects (idk, maybe with separate relations, or collections or w/e), then we need to make sure we 
       # add logic for that in the 'prune_objects' task so that we don't wrongly delete their corresponding activities.
@@ -481,6 +481,69 @@ test "it prunes orphaned activities with the --prune-orphaned-activities" do
 
       assert length(activities) == 4
     end
+
+    test "it prunes orphaned activities with the --prune-orphaned-activities when the objects are referenced from an array" do
+      %Object{} |> Map.merge(%{data: %{"id" => "existing_object"}}) |> Repo.insert()
+      %User{} |> Map.merge(%{ap_id: "existing_actor"}) |> Repo.insert()
+
+      # Multiple objects, one object exists (keep)
+      %Activity{}
+      |> Map.merge(%{
+        local: false,
+        data: %{
+          "id" => "remote_activity_existing_object",
+          "object" => ["non_ existing_object", "existing_object"]
+        }
+      })
+      |> Repo.insert()
+
+      # Multiple objects, one actor exists (keep)
+      %Activity{}
+      |> Map.merge(%{
+        local: false,
+        data: %{
+          "id" => "remote_activity_existing_actor",
+          "object" => ["non_ existing_object", "existing_actor"]
+        }
+      })
+      |> Repo.insert()
+
+      # Multiple objects, one activity exists (keep)
+      %Activity{}
+      |> Map.merge(%{
+        local: false,
+        data: %{
+          "id" => "remote_activity_existing_activity",
+          "object" => ["non_ existing_object", "remote_activity_existing_actor"]
+        }
+      })
+      |> Repo.insert()
+
+      # Multiple objects none exist (prune)
+      %Activity{}
+      |> Map.merge(%{
+        local: false,
+        data: %{
+          "id" => "remote_activity_without_existing_referenced_object",
+          "object" => ["owo", "whats_this"]
+        }
+      })
+      |> Repo.insert()
+
+      assert length(Repo.all(Activity)) == 4
+      Mix.Tasks.Pleroma.Database.run(["prune_objects"])
+      assert length(Repo.all(Activity)) == 4
+      Mix.Tasks.Pleroma.Database.run(["prune_objects", "--prune-orphaned-activities"])
+      activities = Repo.all(Activity)
+      assert length(activities) == 3
+
+      assert "remote_activity_without_existing_referenced_object" not in Enum.map(
+               activities,
+               fn a -> a.data["id"] end
+             )
+
+      assert length(activities) == 3
+    end
   end
 
   describe "running update_users_following_followers_counts" do