Accessing parameters in nested route resources

Phoenix Forum Questions / Help
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1

Hiya! Super new to the Elixir/Phoenix lang (enjoying it so far!). This might be a really silly question, but have had a hard time finding resources/examples.

So I have a nested route resources, e.g.

resources "/users", UserController, except: [:new, :edit] do
  resources "/lists", ListController, except: [:new, :edit]
end

And then in list_controller, just a basic index:

def index(conn, _params) do
  user_lists = Users.list_user_lists()
  render(conn, "index.json", user_lists: user_lists)
end

So I’d like to scope this index to the lists that belong to the user_id in this route. There’s obviously a lot of examples with pulling in the immediate related record, e.g. def show(conn, %{"id" => id}) do which pulls in the current route’s list_id, but how do I also get the user record?

My one work-around so far in the ListController.create( ) action is to pull it out of params, something like

Users.create_list(list_params, Users.get_user!(conn.params["user_id"]))

Is there a better way I’m missing? Thanks!

2

Hi! Excuse the brevity; I’m on my phone. This is also untested and based on a quick read of the controller guide (Controllers — Phoenix v1.7.10) and my possibly incorrect memory. (It’s been a while since I’ve worked on my Elixir/Phoenix project!)

That being said, I think the usual way for your lists controller would be something like:

def index(conn, %{"user_id" => user_id}) do
  user_lists = Users.list_user_lists(user_id)
  render(conn, "index.json", user_lists: user_lists)
end

def show(conn, %{"user_id" => user_id, "id" => id}) do
  list = Users.get_user_list(id)
  render(conn, "show.json", list: list)
end

From the guide:

It is a good practice to pattern match against params in the function signature to provide data in a simple package we can pass on to rendering.

In the show action above, it may not be necessary to include user_id (and its binding to ‘user_id’) in the pattern match, depending on whether or not the user id is needed when getting the list/preparing data for the view.

Related: see the output of mix phx.routes as per Routing — Phoenix v1.7.10 to see the param names of your router’s routes to use in the pattern matching.

3 Likes
3

Ohhh neat, I’ll give that a try, might work a lot nicer.