add parent id for reply

lib/diskuy/forum/post.ex

@@ -7,13 +7,14 @@ defmodule Diskuy.Forum.Post do
     field :points, :integer
     field :thread_id, :id
     field :user_id, :id
+    field :parent_id, :id
     timestamps()
   end
 
   @doc false
   def changeset(post, attrs) do
     post
-    |> cast(attrs, [:message, :points, :thread_id, :user_id])
+    |> cast(attrs, [:message, :points, :thread_id, :user_id, :parent_id])
     |> validate_required([:message, :points, :thread_id, :user_id])
   end
 end

priv/repo/migrations/20201211055930_create_posts.exs

@@ -7,6 +7,7 @@ defmodule Diskuy.Repo.Migrations.CreatePosts do
       add :points, :integer
       add :thread_id, references(:threads, on_delete: :delete_all, type: :id)
       add :user_id, references(:users, on_delete: :delete_all, type: :id)
+      add :parent_id, references(:posts, on_delete: :delete_all, type: :id)
 
       timestamps()
     end