Rendering JSON with views

comment_view.ex

defmodule MyApp.CommentView do
  use MyApp.Web, :view
  @attributes ~W(id name inserted_at)
  
  def render("index.json", %{data: comments}) do
    for comment <- comments, do: render("show.json", %{data: comment})
  end
  
  def render("show.json", %{data: comment}) do
    comment
    |> Map.take(@attributes)
    |> put_assoc(:user, comment.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)
    |> put_assoc(:user, my_model.user)
    # Or you could do
    # |> put_assoc(:user, my_model.user, :lite)
    |> put_assoc(:comments, 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

web.ex

defmodule MyApp.Web do
  def view do
    quote do
      # Default code. 
      
      # You would probably extract these functions to a module.
      def put_assoc(map, :user, user) do
        Map.put(map, :user, UserView.render("show.json", %{data: user})
      end
      
      # Need to customize more?
      def put_assoc(map, :user, user, :lite) do
        Map.put(map, :user, UserView.render("show_lite.json", %{data: user})
      end
      
      def put_assoc(map, :comments, comments) do
        Map.put(map, :comments, CommentView.render("index.json", %{data: comments})
      end
    end
  end
end

I renamed show.json to index.json in the CommentView I think that makes more sense than show.json with a guard checking if it's a list.

I didn't test this so there might be some typos, but I added functions for adding associations more easily. Makes reading what will happen easier. Quicker to scan and see what it's doing. Also easier to use in other views. Still allows for customization and is a bit more imperative.