Composite primary key in Ecto

ecto_migration.exs

defmodule Messaging.Repo.Migrations.CreateGroupChatVersions do
  use Ecto.Migration

  def change do
    create table(:group_chat_versions, primary_key: false) do
      add :group_chat_id, :uuid, primary_key: true
      add :version, :integer, primary_key: true

      timestamps
    end
    create unique_index(:group_chat_versions, [:version, :group_chat_id])
  end
end

group_chat_version.ex

defmodule Messaging.GroupChatVersion do
  use Messaging.Web, :model

  @primary_key false
  schema "group_chat_versions" do
    field :version, :integer, primary_key: true
    field :group_chat_id, UUID5, primary_key: true

    timestamps
  end
  @required_fields ~w(version group_chat_id)
  @optional_fields ~w()

  ...
end