Hi,

I am working on a first elixir project and I am struggling quite a lot with the many_to_many association. I have got it sort-of working using the auto-generated link table, however it does not seem to be checking for uniqueness on the link succesfully.

defmodule KevinCadleFantasyGame.Lineup do
  use Ecto.Schema
  import Ecto.Changeset

  alias KevinCadleFantasyGame.{Player, Repo, Lineup}

  schema "lineups" do
    many_to_many :players, Player,
      join_through: "lineup_players", unique: true

    timestamps()
  end

  @doc false
  def changeset(lineup, attrs) do
    player_ids = if Map.has_key?(attrs, :player_ids), do: attrs.player_ids, else: []
    players = Player.by_ids(player_ids)

    lineup
    |> Repo.preload(:players)
    |> cast(attrs, [:id])
    |> put_assoc(:players, players)
    |> unique_constraint(:players)
    |> validate_required([])
  end


  def create_or_update(params) do
    cs = changeset(%Lineup{}, params)

    if cs.valid? do
      Repo.insert!(cs,
        on_conflict: :nothing,
        conflict_target: :id
        )
    else
      cs
    end
  end
end

and the migration:

defmodule KevinCadleFantasyGame.Repo.Migrations.CreateLineups do
  use Ecto.Migration

  def change do
    create table(:lineups) do

      timestamps()
    end


    create table("lineup_players", primary_key: false) do
      add :player_id, references(:players)
      add :lineup_id, references(:lineups)
    end

    create unique_index(:lineup_players, [:player_id, :lineup_id])
  end
end

With a non-unique link it is giving me a postgres error due to a failure of uniqueness constraint, which is fine, but ideally I’d probably like it to be caught on the changset. What am i doing wrong?

Thanks,

Az