chore: more work on code smell

Co-authored-by: Copilot <copilot@github.com>

lib/bds/posts/post_media.ex

@@ -0,0 +1,40 @@
+defmodule BDS.Posts.PostMedia do
+  @moduledoc false
+
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  @primary_key {:id, :string, autogenerate: false}
+  @foreign_key_type :string
+
+  @type t :: %__MODULE__{
+          id: String.t() | nil,
+          project_id: String.t() | nil,
+          post_id: String.t() | nil,
+          media_id: String.t() | nil,
+          post: term(),
+          media: term(),
+          sort_order: integer() | nil,
+          created_at: integer() | nil
+        }
+
+  schema "post_media" do
+    field :project_id, :string
+
+    belongs_to :post, BDS.Posts.Post, foreign_key: :post_id, references: :id, type: :string
+    belongs_to :media, BDS.Media.Media, foreign_key: :media_id, references: :id, type: :string
+
+    field :sort_order, :integer, default: 0
+    field :created_at, :integer
+  end
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
+  def changeset(post_media, attrs) do
+    post_media
+    |> cast(attrs, [:id, :project_id, :post_id, :media_id, :sort_order, :created_at])
+    |> validate_required([:id, :project_id, :post_id, :media_id, :sort_order, :created_at])
+    |> foreign_key_constraint(:post_id)
+    |> foreign_key_constraint(:media_id)
+    |> unique_constraint([:post_id, :media_id], name: :post_media_post_media_idx)
+  end
+end