How you handling in create method if changeset is not valid?

error is sent to my fallbackController :

defmodule GORprojectWeb.FallbackController do
  @moduledoc """
  Translates controller action results into valid `Plug.Conn` responses.

  See `Phoenix.Controller.action_fallback/1` for more details.
  """
  use GORprojectWeb, :controller

  def call(conn, {:error, :bad_request}) do
    conn
    |> put_status(:bad_request)
    |> render(GORprojectWeb.ErrorView, :"400")
  end

  def call(conn, {:error, :not_found}) do
    conn
    |> put_status(:not_found)
    |> render(GORprojectWeb.ErrorView, :"404")
  end

  def call(conn, {:error, :bad_params}) do
    conn
    |> put_status(:bad_request)
    |> render(GORprojectWeb.ErrorView, :custom, message: "Bad request parameters")
  end

  def call(conn, {:error, :bad_uuid}) do
    conn
    |> put_status(:bad_request)
    |> render(GORprojectWeb.ErrorView, :custom, message: "Bad uuid provided")
  end

  def call(conn, {:error, :bad_id}) do
    conn
    |> put_status(:bad_request)
    |> render(GORprojectWeb.ErrorView, :custom, message: "Bad id provided")
  end

  def call(conn, {:error, changeset}) do
    conn
    |> put_status(:unprocessable_entity)
    |> render(GORprojectWeb.ChangesetView, "error.json", changeset: changeset)
  end
end

Fall back controller is okay but its better if you use the error_view file for displaying changeset errors.

 def render("errors.json", %{code: code, message: message, changeset: changeset}) do
    %{error: %{code: code, message: message, errors: translate_errors(changeset)}}
  end

 def translate_errors(changeset) do
   Ecto.Changeset.traverse_errors(changeset, &translate_error/1)
end

you can pass your invalid changeset to this and it will display an error from that changeset .

I added your code in my error_view.ex, and it seems like the error is not handled there. From the stacktrace it seems that it goes from room_controller directly to changeset_view, in which there is :

  def translate_errors(changeset) do
    Ecto.Changeset.traverse_errors(changeset, &translate_error/1)
  end

  def render("error.json", %{changeset: changeset}) do
    # When encoded, the changeset returns its errors
    # as a JSON object. So we just pass it forward.
    %{errors: translate_errors(changeset)}
  end

From stacktrace it seems like in error helpers the translate_error function is not working for your is invalid message. You are passing one argument but it accepts 2 arguments.

I totally agree with you, and this is where i do not understand. In my errors.pot, i have the following code :

## From Ecto.Changeset.put_change/3
msgid "is invalid"
msgstr ""

According to this thread, it should be working

what is your goal? What you trying to implement?

I am trying to understand why this error is raised, how to handle it properly, and of course i am trying to fix the Repo.insert error

note that the error is not raised anymore if i delete father: {} inside

  def create_room(attrs \\ %{}) do
    %Room{children: [], father: {}, users: []}
    |> Room.changeset(attrs)
    |> Repo.insert()
  end

But i then have the following error :

error] #PID<0.594.0> running GORprojectWeb.Endpoint (cowboy_protocol) terminated
Server: localhost:4000 (http)
Request: POST /api/rooms
** (exit) an exception was raised:
    ** (Protocol.UndefinedError) protocol Enumerable not implemented for %GORproject.Rooms.Room{__meta__: #Ecto.Schema.Metadata<:loaded, "rooms">, children: [], depth: 1, description: nil, father: #Ecto.Association.NotLoaded<association :father is not loaded>, father_id: nil, id: 25, inserted_at: ~N[2018-10-01 09:52:22.729960], name: "Accueillir", public: false, updated_at: ~N[2018-10-01 09:52:22.733056], users: []}. 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
        (elixir) /private/tmp/elixir-20180825-48782-1ofrgzr/elixir-1.7.3/lib/elixir/lib/enum.ex:1: Enumerable.impl_for!/1
        (elixir) /private/tmp/elixir-20180825-48782-1ofrgzr/elixir-1.7.3/lib/elixir/lib/enum.ex:141: Enumerable.reduce/3
        (elixir) lib/enum.ex:2979: Enum.reduce/3
        (gor_project) lib/gor_project_web/router.ex:1: GORprojectWeb.Router.Helpers.segments/3
        (gor_project) lib/gor_project_web/router.ex:1: GORprojectWeb.Router.Helpers.room_path/3
        (gor_project) lib/gor_project_web/controllers/room_controller.ex:22: GORprojectWeb.RoomController.create/2
        (gor_project) lib/gor_project_web/controllers/room_controller.ex:1: GORprojectWeb.RoomController.action/2
        (gor_project) lib/gor_project_web/controllers/room_controller.ex:1: GORprojectWeb.RoomController.phoenix_controller_pipeline/2
        (gor_project) lib/gor_project_web/endpoint.ex:1: GORprojectWeb.Endpoint.instrument/4
        (phoenix) lib/phoenix/router.ex:278: Phoenix.Router.__call__/1
        (gor_project) lib/gor_project_web/endpoint.ex:1: GORprojectWeb.Endpoint.plug_builder_call/2
        (gor_project) lib/gor_project_web/endpoint.ex:1: GORprojectWeb.Endpoint.call/2
        (plug) lib/plug/adapters/cowboy/handler.ex:16: Plug.Adapters.Cowboy.Handler.upgrade/4
        (cowboy) /Users/giom/Documents/develop/web/GORProject-API/deps/cowboy/src/cowboy_protocol.erl:442: :cowboy_protocol.execute/4

Add IO.inspect after |> Room.changeset(attrs)

      def create_room(attrs \\ %{}) do
       %Room{children: [], father: {}, users: []}
       |> Room.changeset(attrs)
       |> IO.inspect()
       |> Repo.insert()
      end

And see what it gives you in the console. After you run this method

i’ve put two IO.inspect :

  def create_room(attrs \\ %{}) do
    %Room{children: [], father: {}, users: []}
    |> Room.changeset(attrs)
    |> IO.inspect()
    |> Repo.insert()
    |> IO.inspect()
  end

and i have :

[info] POST /api/rooms
[debug] Processing with GORprojectWeb.RoomController.create/2
  Parameters: %{"room" => %{"depth" => 1, "name" => "Accueillir", "public" => false}}
  Pipelines: [:api, :auth_api]
#Ecto.Changeset<
  action: nil,
  changes: %{depth: 1, name: "Accueillir", public: false},
  errors: [],
  data: #GORproject.Rooms.Room<>,
  valid?: true
>
[debug] QUERY OK db=0.3ms
begin []
[debug] QUERY OK db=0.2ms
rollback []
{:error,
 #Ecto.Changeset<
   action: :insert,
   changes: %{depth: 1, name: "Accueillir", public: false},
   errors: [father: "is invalid"],
   data: #GORproject.Rooms.Room<>,
   valid?: false
 >}

followed by the error stacktrace