elixir ecto - 具有多个模式的 embed_one

Question

我有一个 item 表，我希望它有多个 embedded schema，例如:

  schema "items" do
    field :name, :string
    field :type, :string

    #embed_one with :either, I found this somewhere online but can't get the doc anywhere.
    embeds_one :details, either: [ Product, Service], on_replace: :update

  @doc false
  def changeset(item, attrs) do
    item
    |> cast(attrs, [:name, :type, :description, :publish, :user_id])
    |> details_by_type(attrs[:type], :details)
  end

  #psuedo code of cast_embed
  defp details_by_type(item, type, details) do
    case type do
      :product -> item |> #cast_embed of :details to Product
      :service -> item |> #cast_embed of :details to Service
    end
  end

基本上，我想要一个details field(:map) 来根据项目的类型保留不同的嵌入式模式。但我无法让它工作。我不断收到这样的错误:

(ArgumentError) you attempted to apply a function on [either:[OkBackend.Items.Task, OkBackend.Items.Product,OkBackend.Items.Service], on_replace: :update]. Modules (the firstargument of apply) must always be an atom

这样做的正确方法是什么？

Answer 1

看起来这个包就是您要找的，这是文档中的示例:

defmodule MyApp.Reminder do
  use Ecto.Schema
  import Ecto.Changeset
  import PolymorphicEmbed, only: [cast_polymorphic_embed: 3]

  schema "reminders" do
    field :date, :utc_datetime
    field :text, :string

    field :channel, PolymorphicEmbed,
      types: [
        sms: MyApp.Channel.SMS,
        email: [module: MyApp.Channel.Email, identify_by_fields: [:address, :confirmed]]
      ],
      on_type_not_found: :raise,
      on_replace: :update
  end

  def changeset(struct, values) do
    struct
    |> cast(values, [:date, :text])
    |> cast_polymorphic_embed(:channel, required: true)
    |> validate_required(:date)
  end
end

https://hexdocs.pm/polymorphic_embed/readme.html