Phoenix 不呈现关联

Question

我有一个简单的Todo/Author/Comment

Todo has_many comments
Comment belongs_to Todo
Todo belongs_to Author
Author has_many todos
Author has_many comments
Comment belongs_to Author

如果我这样渲染 todo_view.ex：

  def render("todo.json", %{todo: todo}) do
    %{id: todo.id,
      title: todo.title,
      description: todo.description,
      date: todo.date,
      author: author_json(todo.author)}
  end
  defp author_json(author) do
    %{name: author.name}
  end

当我访问 /api/todos 和 /api/comments 时一切正常但是如果我想添加待办事项的评论列表：

  def render("todo.json", %{todo: todo}) do
    %{id: todo.id,
      title: todo.title,
      description: todo.description,
      date: todo.date,
      author: author_json(todo.author),
      comments: render_many(todo.comments, CommentView, "comment.json")}
  end

我在 comment_view.ex

中遇到 KeyError

key :name not found in: #Ecto.Association.NotLoaded

  def render("comment.json", %{comment: comment}) do
    %{id: comment.id,
      content: comment.content,
      author: author_json(comment.author)}
  end
  defp author_json(author) do
    %{name: author.name}
  end

不知何故，Elixir 在查询待办事项时看不到评论/作者关联，但在查询评论时确实看到了。

我为评论做了预加载：

comments = Repo.all(Comment) |> Repo.preload(:author)

知道这里发生了什么吗？

Answer 1

当您从数据库中获取 todos 时，您是否预加载了 author？像这样：

todos = Todo |> Repo.all() |> Repo.preload([comments: [:author]])

这会为所有 ToDos 加载 Comments 及其 Author 关联。

Phoenix 不呈现关联

Phoenix doesn't render associations

elixir

phoenix-framework