Ecto equivalent for Rails' acts_as_list?

Question

For Rails, there is the excellent acts_as_list gem, which allows the definition of has-many associations that are ordered by an position integer field. Is there a similar library for Ecto and Phoenix, or does Ecto even implement something like that itself?

Answer 1

Looks like there's a small Ecto extension that could help: https://github.com/zovafit/ecto-ordered

---

Though (at least the ordering part of) this could be accomplished fairly easily using some Ecto basics alone:

web/models/invoice.ex

defmodule MyApp.Invoice do
  use MyApp.Web, :model

  schema "invoices" do
    has_many :line_items, MyApp.LineItem

    timestamps
  end

  # ...
end

web/models/line_item.ex

defmodule MyApp.LineItem do
  use MyApp.Web, :model

  schema "line_items" do
    belongs_to :invoice, MyApp.Invoice
    field :position, :integer

    timestamps
  end

  def positioned do
    from l in __MODULE__,
    order_by: [asc: l.position]
  end

  # ...
end

Then you could query your positioned items like so:

Repo.all(MyApp.LineItem.positioned)

Or preload them like so:

Repo.get(MyApp.Invoice, id) |> Repo.preload(line_items: MyApp.LineItem.positioned)

You can read some context about including scopes or conditions into Ecto.Schema.has_many/3 here: https://github.com/elixir-lang/ecto/issues/659