为自引用Ecto模型构建JSON映射

I have an Ecto model as such:

我有一个Ecto模型：

defmodule Project.Category do
  use Project.Web, :model

  schema "categories" do
    field :name, :string
    field :list_order, :integer
    field :parent_id, :integer
    belongs_to :menu, Project.Menu
    has_many :subcategories, Project.Category, foreign_key: :parent_id
    timestamps
  end

  @required_fields ~w(name list_order)
  @optional_fields ~w(menu_id parent_id)

  def changeset(model, params \ :empty) do
    model
    |> cast(params, @required_fields, @optional_fields)
  end
end
d