Using UUIDs with Postgres in Phoenix and Ecto

September 22, 2016

Setting up Ecto to use UUIDs instead of the regular integer serial IDs with PostgreSQL in Phoenix has always been a hassle, as evident from the numerous blog posts and Stackoverflow questions (1, 2, 3, …). But as of Ecto v2 and Phoenix v1.1, you can pass --binary-id when creating a new Phoenix project to automatically use UUIDs (or other binary IDs when using different databases and adapters).

When creating a new project with --binary-id, it will automatically set appropriate values for @primary_key and @foreign_key_type in your web/web.ex. For Postgres, this means using Ecto.UUID at the back (Ecto handles this automatically):

def model do
  quote do
    use Ecto.Schema

    import Ecto
    import Ecto.Changeset
    import Ecto.Query

    @primary_key {:id, :binary_id, autogenerate: true}
    @foreign_key_type :binary_id
  end
end

Existing Applications

If you want to start using UUIDs in your existing Phoenix application, you need to specify :binary_id in your Ecto migration in addition to the model method above in web/web.ex:

create table(:posts, primary_key: false) do
  add :id, :binary_id, primary_key: true
end

For a more detailed solution for existing Phoenix apps, see the Ecto Schema Docs or José’s answer on Stackoverflow.