feat: more completeness of spec and start at embedding

lib/bds/posts/link.ex

@@ -0,0 +1,25 @@
+defmodule BDS.Posts.Link do
+  @moduledoc false
+
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  @primary_key {:id, :string, autogenerate: false}
+  @foreign_key_type :string
+
+  schema "post_links" do
+    belongs_to :source_post, BDS.Posts.Post, foreign_key: :source_post_id, references: :id, type: :string
+    belongs_to :target_post, BDS.Posts.Post, foreign_key: :target_post_id, references: :id, type: :string
+
+    field :link_text, :string
+    field :created_at, :integer
+  end
+
+  def changeset(link, attrs) do
+    link
+    |> cast(attrs, [:id, :source_post_id, :target_post_id, :link_text, :created_at])
+    |> validate_required([:id, :source_post_id, :target_post_id, :created_at])
+    |> foreign_key_constraint(:source_post_id)
+    |> foreign_key_constraint(:target_post_id)
+  end
+end