comment_view.ex

defmodule MyApp.CommentView do                                                                                                                                                                  
  use MyApp.Web, :view
  @attributes ~W(id name inserted_at)
  
  def render("show.json", %{data: comments}) when is_list(comments) do
    for comment <- comments do
      render("show.json", data: comment)
    end
  end
  
  def render("show.json", data: comment) do
    comment
    |> Map.take(@attributes)
    |> Map.put(:user, UserView.render('show_lite.json', data: data.user)
  end
end

mymodel_view.ex

defmodule MyApp.MyModelView do                                                                                                                                                                  
  use MyApp.Web, :view
  @attributes ~W(id body title inserted_at)
  
  def render("show.json", %{data: my_model})
    my_model
    |> Map.take(@attributes)
    |> Map.update!(:title, &String.capitalize)
    |> Map.put(:user, UserView.render("show.json", data: my_model.user)
    |> Map.put(:comments, CommentView.render("show.json", data: my_model.comments)
  end
end

user_view.ex

defmodule MyApp.UserView do                                                                                                                                                                  
  use MyApp.Web, :view
  @attributes ~W(id name inserted_at)
  
  def render("show.json", %{data: user})    
    render("show_lite.json", data: user)
    |> Map.put(:image, ImageView.render("show.json", data: user.image)
  end
  
  def render("show_lite.json", data: user)    
    user
    |> Map.take(@attributes)
  end
end

Great examples. You need to add a modifier to @attributes list to make it work with Map.take method. It accepts only list of atoms, not strings as it is in your example. Please update your post, because it on the top of "phoenix json views" query searches in search engine.

Best regards