Using a slug as your primary key with Elixir's Ecto and Phoenix

create_table.exs

# add the following line add :id, :string, primary_key: true 
#
#
defmodule CheckpointCharlie.Repo.Migrations.CreatePlayers do
  use Ecto.Migration

  def change do
    create table(:players, primary_key: false) do
      add :id, :string, primary_key: true  ## 
      add :name, :string
      add :position, :string
      add :number, :integer

      timestamps()
    end

  end
end

mix.exs

# One: Add lib https://github.com/sobolevn/ecto_autoslug_field to your deps...  ... then mix deps.get

  defp deps do
    [
      {:phoenix, "~> 1.4.2"},
      {:phoenix_pubsub, "~> 1.1"},
      {:phoenix_ecto, "~> 4.0"},
      {:ecto_sql, "~> 3.0"},
      {:postgrex, ">= 0.0.0"},
      {:ecto_autoslug_field, "~> 1.0"} # <-- add this
    ]
  end

player.ex

#
# mix phx.gen.json PlayPen Player players name:string position:string number:integer
#

defmodule CheckpointCharlie.PlayPen.Player do
  use Ecto.Schema
  import Ecto.Changeset

  alias CheckpointCharlie.PlayPen.Slug

  #  Override the default primary key settings 
  #  see https://phoenixframework.org/blog/custom-primary-key
  #
  @primary_key {:id, Slug.Type, []}
  @derive {Phoenix.Param, key: :id}
  schema "players" do
    field :name, :string
    field :number, :integer
    field :position, :string

    timestamps()
  end

  @doc false
  def changeset(player, attrs) do
    player
    |> cast(attrs, [:name, :position, :number])
    |> validate_required([:name, :position, :number])
    |> validate_format(:name, ~r/^\w+\/\w/, message: "must be in the format: group/name", trim: true) 
    #
    # Add this see https://hexdocs.pm/ecto_autoslug_field/readme.html
    |> Slug.maybe_generate_slug  
    |> Slug.unique_constraint
  end
end

players.json

#
# curl http://127.0.0.1:4000/api/player | python -m json.tool
#
{
    "data": [
        {
            "id": "wally-nelson",
            "name": "Wally Nelson",
            "number": 2,
            "position": "forward"
        }
    ]
}

Slug.ex

#
# Define a simple slug type stating the source for the slug and the primary key field name
# see documention https://hexdocs.pm/ecto_autoslug_field/readme.html
#

defmodule CheckpointCharlie.PlayPen.Slug do
    use EctoAutoslugField.Slug, from: :name, to: :id
end