Use unique index to prevent duplicate items from being created

lib/frenzy/item.ex

@@ -83,5 +83,10 @@ defmodule Frenzy.Item do
     item
     |> cast(attrs, [:guid, :title, :url, :creator, :date, :content, :read, :read_date, :tombstone])
     |> validate_required([:guid, :url, :date, :content, :feed])
+    |> unique_constraint(:items_feed_guid_index)
+  end
+
+  def exists?(feed_id, guid) do
+    Frenzy.Repo.exists?(__MODULE__, feed_id: feed_id, guid: guid)
   end
 end

lib/frenzy/task/create_item.ex

@@ -62,7 +62,7 @@ defmodule Frenzy.Task.CreateItem do
       end
 
     case result do
-      {:err, error} ->
+      {:error, error} ->
         Logger.error(error)
 
       {:ok, item_params} ->

lib/frenzy/update_feeds.ex

@@ -158,11 +158,9 @@ defmodule Frenzy.UpdateFeeds do
       FetchFavicon.run(feed)
     end
 
-    feed = Repo.preload(feed, [:items])
-
     Enum.each(rss.items, fn entry ->
       # todo: use Repo.exists for this
-      if !Enum.any?(feed.items, fn item -> item.guid == entry.guid end) do
+      unless Item.exists?(feed.id, entry.guid) do
         CreateItem.start_link(feed, entry)
       end
     end)

priv/repo/migrations/20210908133238_creat_item_unique_index.exs

@@ -0,0 +1,7 @@
+defmodule Frenzy.Repo.Migrations.CreatItemUniqueIndex do
+  use Ecto.Migration
+
+  def change do
+    create unique_index(:items, [:feed_id, :guid], name: :items_feed_guid_index)
+  end
+end