Elixir 如何预加载关联？

我有下面的外胚层模型。当我试图渲染时，我得到一个错误。我如何修改@derive使其能够预加载？还是我必须写下实施方案？建议的处理方法是什么

** (RuntimeError) cannot encode association :tilemap_layers from MyProject.Tilemap to JSON because the association was not loaded. Please make sure you have preloaded the association or remove it from the data to be encoded

模型如下：

defmodule MyProject.Tilemap do
  use MyProject.Web, :model

  @derive {Poison.Encoder, only: [
    :name,
    :tile_width,
    :tile_height,
    :width,
    :height,
    :orientation,
    :tilemap_layers,
    :tilesets
  ]}

  schema "tilemaps" do

    field :name, :string
    field :tile_width, :integer
    field :tile_height, :integer
    field :width, :integer
    field :height, :integer
    field :orientation, :string

    has_many :tilemap_layers, MyProject.TilemapLayer
    has_many :tilesets, MyProject.Tileset

    timestamps
  end

  @required_fields ~w(tile_width tile_height width height)
  @optional_fields ~w()

  @doc """
  Creates a changeset based on the `model` and `params`.

  If no params are provided, an invalid changeset is returned
  with no validation performed.
  """
  def changeset(model, params \\ :empty) do
    model
    |> cast(params, @required_fields, @optional_fields)
  end
end

---

简而言之，你不应该这样做。预加载数据不是视图层的责任

在获取资源（通常是控制器或从控制器调用的函数）时，应该执行预加载

例如，使用：

您还可以使用以下命令在查询中执行预加载：

---

谢谢你，加兹勒，现在说得通了！

def index(_conn, _params)
  timemaps = Tilemap |> Repo.all() |> Repo.preload(:timemap_layers)
  render("index.json", tilemaps: tilemaps)
end

query = from t in Tilemap,
  preload: [:tilemap_layers]
Repo.all(query)