added an endpoint for getting unread notification count

priv/repo/migrations/20200415181818_update_markers.exs

@@ -0,0 +1,40 @@
+defmodule Pleroma.Repo.Migrations.UpdateMarkers do
+  use Ecto.Migration
+  import Ecto.Query
+  alias Pleroma.Repo
+
+  def up do
+    update_markers()
+  end
+
+  def down do
+    :ok
+  end
+
+  defp update_markers do
+    now = NaiveDateTime.utc_now()
+
+    markers_attrs =
+      from(q in "notifications",
+        select: %{
+          timeline: "notifications",
+          user_id: q.user_id,
+          last_read_id:
+            type(fragment("MAX( CASE WHEN seen = true THEN id ELSE null END )"), :string)
+        },
+        group_by: [q.user_id]
+      )
+      |> Repo.all()
+      |> Enum.map(fn %{last_read_id: last_read_id} = attrs ->
+        attrs
+        |> Map.put(:last_read_id, last_read_id || "")
+        |> Map.put_new(:inserted_at, now)
+        |> Map.put_new(:updated_at, now)
+      end)
+
+    Repo.insert_all("markers", markers_attrs,
+      on_conflict: {:replace, [:last_read_id]},
+      conflict_target: [:user_id, :timeline]
+    )
+  end
+end