Just saw this blog post by @leejarvis: https://leejarvis.me/posts/2020/phoenix-simplify-nested-resources

The post explains how to resolve nested resources in a central place.

post_comment_path  GET     /projects/:project_id/posts/:post_id/comments           AppWeb.CommentController :index
post_comment_path  GET     /projects/:project_id/posts/:post_id/comments/:id/edit  AppWeb.CommentController :edit
post_comment_path  GET     /projects/:project_id/posts/:post_id/comments/new       AppWeb.CommentController :new

[…] every one of our controller actions are going to need to handle this project_id parameter.

I come from a Rails background, and the canonical way to solve this in Rails is to add a before_action:

class CommentController
  before_action :set_project

  # actions

  def set_project
    @project = Project.find(params[:project_id])
  end
end

The author then uses a custom Plug to add the project to conn.assigns:

defmodule AppWeb.CommentController do
  use AppWeb, :controller

  plug :put_project

  def show(conn, %{"post_id" => post_id, "id" => comment_id}) do
    %{current_project: project} = conn.assigns
    render(conn, "show.html", comment: get_comment!(project, post_id, comment_id))
  end

  defp put_project(conn, _opts) do
    current_project = fetch_current_project(conn.params["project_id"])
    assign(conn, :current_project, current_project)
  end
end

I am curious about your opinions. How do you handle this in your projects?