Protocol Enumerable not implemented for

I am trying to implement my new.html.eex file to create new posts on my website.


<h1>Create Post</h1>
<%= form_for @changeset, post_path(@conn, :create,, fn f -> %>
  <%= if @changeset.action do %>
    <div class="alert alert-danger">
      <p>There are some errors</p>
  <% end %>
  <div class="form-group">
    <%= text_input f, :title, placeholder: "Title",
                              class: "form-control" %>
    <%= error_tag f, :title %>
  <div class="form-group">
    <%= textarea f, :body, placeholder: "Body", class: "form-control" %>
    <%= error_tag f, :body %>
  <%= submit "Create post", class: "btn btn-primary" %>
<% end %>

new and create methods in post_controller.ex:

  def new(conn, _params, current_user) do
    changeset =
    |> Ecto.build_assoc(:posts)
    |> Post.changeset
    render conn, "new.html", changeset: changeset

  def create(conn, %{"post" => post_params}, current_user) do
    changeset =
    |> Ecto.build_assoc(:posts)
    |> Post.changeset(post_params)
    case Repo.insert(changeset) do
      {:ok, _} ->
        |> put_flash(:info, "Post was created successfully")
        |> redirect(to: post_path(conn, :index,
        {:error, changeset} ->
          render(conn, "new.html", changeset: changeset)

But I can’t access the template. I get the following error:

protocol Enumerable not implemented for 1. This protocol is implemented for: DBConnection.PrepareStream, DBConnection.Stream, Date.Range, Ecto.Adapters.SQL.Stream, File.Stream, Function, GenEvent.Stream, HashDict, HashSet, IO.Stream, List, Map, MapSet, Postgrex.Stream, Range, Stream

Things seems to get wrong in the router, so here is my router.ex:

defmodule GazetteWeb.Router do
  use GazetteWeb, :router

  pipeline :browser do
    plug :accepts, ["html"]
    plug :fetch_session
    plug :fetch_flash
    plug :protect_from_forgery
    plug :put_secure_browser_headers

  pipeline :api do
    plug :accepts, ["json"]

  pipeline :with_session do #if a user is signed in
    plug Guardian.Plug.VerifySession
    plug Guardian.Plug.LoadResource
    plug Gazette.CurrentUser

  pipeline :admin_required do
    plug Gazette.CheckAdmin

  pipeline :login_required do


  scope "/posts", GazetteWeb do
    pipe_through [:browser, :with_session, :admin_required]
    resources "/", PostController, except: [:index, :show]

  scope "/", GazetteWeb do
    pipe_through [:browser, :with_session]

    get "/", PageController, :index

    resources "/users", UserController, only: [:show, :new, :create]
    resources "/sessions", SessionController, only: [:new, :create, :delete]
    resources "/posts", PostController, only: [:index, :show]

  # Other scopes may use custom stacks.
  # scope "/api", GazetteWeb do
  #   pipe_through :api
  # end

any Idea ?

Can you show the stacktrace or full error? Somewhere in your code there is a call to a function from Enum module with 1 instead of something it supports. A stacktrace would help find the place where this call happens, maybe.

the stacktrace:

 elixir /private/tmp/elixir-20180111-94038-1oxcohh/elixir-1.5.3/lib/elixir/lib/enum.ex:1 Enumerable.impl_for!/1
 elixir /private/tmp/elixir-20180111-94038-1oxcohh/elixir-1.5.3/lib/elixir/lib/enum.ex:116 Enumerable.reduce/3
 elixir lib/enum.ex:1850 Enum.reduce/3
 lib/gazette_web/router.ex:1 GazetteWeb.Router.Helpers.segments/3
 lib/gazette_web/router.ex:1 GazetteWeb.Router.Helpers.post_path/3
 lib/gazette_web/templates/post/new.html.eex:2 GazetteWeb.PostView."new.html"/1
 lib/gazette_web/templates/layout/app.html.eex:26 GazetteWeb.LayoutView."app.html"/1
 phoenix lib/phoenix/view.ex:332 Phoenix.View.render_to_iodata/3
 phoenix lib/phoenix/controller.ex:740 Phoenix.Controller.do_render/4
 lib/gazette_web/controllers/post_controller.ex:1 GazetteWeb.PostController.action/2
 lib/gazette_web/controllers/post_controller.ex:1 GazetteWeb.PostController.phoenix_controller_pipeline/2
 lib/gazette_web/endpoint.ex:1 GazetteWeb.Endpoint.instrument/4
 phoenix lib/phoenix/router.ex:278 Phoenix.Router.__call__/1
 lib/gazette_web/endpoint.ex:1 GazetteWeb.Endpoint.plug_builder_call/2
 lib/plug/debugger.ex:99 GazetteWeb.Endpoint."call (overridable 3)"/2
 plug lib/plug/adapters/cowboy/handler.ex:15 Plug.Adapters.Cowboy.Handler.upgrade/4
  • UPDATE: I got it working by removing @current_user from the controller and the template.

However, I am wondering if it works right: here is my DB:

iex(2)> Gazette.Repo.all(Gazette.Post)
[debug] QUERY OK source="posts" db=3.2ms decode=5.6ms
SELECT p0."id", p0."body", p0."title", p0."user_id", p0."inserted_at", p0."updated_at" FROM "posts" AS p0 []
[%Gazette.Post{__meta__: #Ecto.Schema.Metadata<:loaded, "posts">,
  body: "Alors voici mon tout premier post. J'espère qu'il en appellera bien d'autres, de bonne qualité et plaisant pour les lecteurs. J'ai hâte que tout cela démarre ! ",
  id: 1, inserted_at: ~N[2018-02-12 17:05:54.966289],
  title: "Mon tout Premier Post !! ",
  updated_at: ~N[2018-02-12 17:05:54.966325],
  user: #Ecto.Association.NotLoaded<association :user is not loaded>,
  user_id: 1},

What is this user: #Ecto.Association.NotLoaded<association :user is not loaded>, ??

What is this user: #Ecto.Association.NotLoaded, ??

It’s something like a placeholder. It allows for lazy-loading resources.

1 Like

The problem seems to be that post_path(@conn, :create, accepts 3 arguments, where the last is a list of options. So you should probably change it to post_path(@conn, :create).

With options it would be

post_path(@conn, :create, to: "a", by: "b")
# which is the same as
post_path(@conn, :create, [to: "a", by: "b"])
# which is the same as
post_path(@conn, :create, [{:to, "a"}, {:by, "b"}])
# and results in
1 Like

OK thank you ! I guess it now works as expected

But then How do I access to the user from post ? e.g. does not seem to work

You would first need to preload it.

For example,

Repo.preload(post, :user)