Where the :id in a route comes from?

Hi all,

I am following along the excellent Phoenix in Action book from @geo. In page 59, while he takes us through the life cycle of a request through Phoenix, he says:

from our list of routes, /posts/:id is the path that gets you to this function. The “:id” portion of that route specifies that whatever you put into that position will be passed as the id in the params map.

But when I look at scopes in the router.ex (or the endpoint.ex file before that), I do not see the :id portion anywhere.

defmodule BlogWeb.Router do
  # ...
  scope "/", BlogWeb do
    pipe_through :browser

    get "/", PageController, :index
    resources "/posts", PostController do
      resources "/comments", CommentController, only: [:create]

  scope "/api", BlogWeb.API do
    pipe_through :api

    resources "/posts", PostController, only: [:index, :show]

Is it supposed to be implied anywhere? How about if I do not what the id but another parameter. Or am I not understanding the philosophy of it?

Thanks very much!


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Your id will come from the database using a function like this in a context


def get_customer(id) do
   |> Repo.get(id)

Then this function will be called in a controller.

To u8nderstand this better follow the phoenix guide here https://hexdocs.pm/phoenix/overview.html

ohhh… right, reading the documentation helps. Sorry about that. So, for what I understand if I want to use another parameter what I need is to define a helper. Let’s say I have a table like this:

id      product_code
1      1001
2      1002
3      4569

and I want to be able to filter by product_code, then I would need something like this?

get "/api/:product_code", ApiController, :show

I understand it wil automatically generate this:

MyAppWeb.Router.Helpers.api_path(conn_or_endpoint, :show, "hello", some: "query")

Am I correct?


OK, that helps. Thank you! I do not see any of that in the provided code but as @LostKobrakai points out, it seems to be implicit. I will read the whole thing carefully to better understand the concept. Thanks again for replying.

To be able to access the resources route you need to have:

  • a migration
  • a schema
  • a controller
  • a view
  • a template.

So you use a mix generator to do that for you but those things need to exist to be able to use the resource route.

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The following command might be useful if You want to inspect your routes.

$ mix phx.routes
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