Elixir association help

I see this is very helpful.
Thanks for the ressource !

If you’re trying to debug what’s happening you should use IO.inspect instead of IO.puts:

def call(conn, {:error, changeset}) do
  IO.inspect(changeset, label: "changeset")
  IO.inspect(conn, label: "conn")
end

More info at:

• IO — Elixir v1.20.2
• https://elixir-lang.org/getting-started/debugging.html

Well, glad to hear things are working.

Just as a reference, to start debugging a changeset problem you can look at the errors key, which correspond to which of your changeset validations failed. So for example, your changeset had:

errors: [name: {"can't be blank", [validation: :required]}]

I do not understand what happened but it seems that the association is working fine now.. I just recompile the project and it worked.

So that’s great, and thanks to help of this wonderful community that motivates the envy of persisting !

Now my second step is to see the associated images on GET /categories route !

First of all thanks a lot for this great explanation I think I’m getting it a little bit more.

If I want to pattern match through the changeset against Ecto.Changeset{} the documentation doesn’t specify how to format ecto response in order to debug it..

I have created a second call function :

 def call(conn, {:error, changeset}) do
    IO.puts(Plug.Conn.Status.code/1)
    IO.puts(changeset)
  end

In order to get which status code is sent back from the error but it still trying to call Plug.Conn.Status.code/0
And also getting the changeset pattern used by Ecto and the printed output was:

#Ecto.Changeset<action: :insert, changes: %{category: #Ecto.Changeset<action: :insert, changes: %{}, errors: [name: {"can't be blank", [validation: :required]}], data: #ApiApp.Images.Categories<>, valid?: false>, description: "This is a test image", image: "mylovelywife.png", name: "i1"}, errors: [category_id: {"can't be blank", [validation: :required]}]

Thanks again for everything mate !

So, in your controller you have create/2 where you catch the happy path in the with clause. What I think is happening here is that you are actually getting a changeset error that isn’t being handled. The reason I think this is the case is because of the fallback controller function definition error.

You don’t have an else clause for the with so create/2 is just returning the {:error, changeset} of Repo.insert() in create_image/1. But, {:error, changeset} isn’t a valid %Plug.Conn{} struct – the expected return of your controller functions!

Since you’re not returning a %Plug.Conn{}, Phoenix tries to help you out and call your defined fallback controller ApiAppWeb.FallbackController. You are likely missing the function call(conn, {:error, changeset}) there (you might want to pattern match against the changeset against %Ecto.Changeset{} to avoid a catch all match…)

So you have a couple options to debug from here. You can define the fallback controller call/2 and inspect in there, or put an inspect in your changeset pipeline to see what’s going wrong. (The error is actually in the previous error you posted, at the very end of the line)

I know this is a lot so let me know if you have any questions! Also here’s the documentation on the fallback controller with good examples!

Oh and here is the fallbackController :

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

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

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

Yeah for sure !

here you go :

defmodule ApiAppWeb.ImageController do
  use ApiAppWeb, :controller

  alias ApiApp.Images
  alias ApiApp.Images.Image

  action_fallback ApiAppWeb.FallbackController

  def index(conn, _params) do
    image = Images.list_image()
    render(conn, "index.json", image: image)
  end

  def create(conn, %{"image" => image_params}) do
    with {:ok, %Image{} = image} <- Images.create_image(image_params) do
      conn
      |> put_status(:created)
      |> put_resp_header("location", Routes.image_path(conn, :show, image))
      |> render("show.json", image: image)
    end
  end

  def show(conn, %{"id" => id}) do
    image = Images.get_image!(id)
    render(conn, "show.json", image: image)
  end

  def update(conn, %{"id" => id, "image" => image_params}) do
    image = Images.get_image!(id)

    with {:ok, %Image{} = image} <- Images.update_image(image, image_params) do
      render(conn, "show.json", image: image)
    end
  end

  def delete(conn, %{"id" => id}) do
    image = Images.get_image!(id)

    with {:ok, %Image{}} <- Images.delete_image(image) do
      send_resp(conn, :no_content, "")
    end
  end
end

and the method create_image:

  def create_image(attrs \\ %{}) do
    %Image{}
    |> Image.changeset(attrs)
    |> Ecto.Changeset.cast_assoc(:category, with: &Categories.changeset/2)
    |> Repo.insert()
  end

Thanks a lot for helping me mate !

Can you share the contents of api_app_web/controllers/image_controller.ex?

Yes you’re right I was just making an update about it the right module to use is the Categories module and not category.

But now the problem comes from the fallback controller…

 [info] POST /api/image
phoenix_1  | [debug] Processing with ApiAppWeb.ImageController.create/2
phoenix_1  |   Parameters: %{"image" => %{"category" => %{"id" => 1}, "description" => "This is a test image", "image" => "mylovelywife.png", "name" => "i1"}}
phoenix_1  |   Pipelines: [:api]
phoenix_1  | [info] Sent 500 in 1ms
phoenix_1  | [info] Converted error :function_clause to 500 response
phoenix_1  | [error] #PID<0.910.0> running ApiAppWeb.Endpoint (connection #PID<0.909.0>, stream id 1) terminated
phoenix_1  | Server: localhost:4000 (http)
phoenix_1  | Request: POST /api/image
phoenix_1  | ** (exit) an exception was raised:
phoenix_1  |     ** (FunctionClauseError) no function clause matching in ApiAppWeb.FallbackController.call/2
phoenix_1  |         (api_app 0.1.0) lib/api_app_web/controllers/fallback_controller.ex:9: ApiAppWeb.FallbackController.call(%Plug.Conn{adapter: {Plug.Cowboy.Conn, :...}, assigns: %{}, before_send: [#Function<0.24098476/1 in Plug.Telemetry.call/2>], body_params: %{"image" => %{"category" => %{"id" => 1}, "description" => "This is a test image", "image" => "mylovelywife.png", "name" => "i1"}}, cookies: %Plug.Conn.Unfetched{aspect: :cookies}, halted: false, host: "localhost", method: "POST", owner: #PID<0.910.0>, params: %{"image" => %{"category" => %{"id" => 1}, "description" => "This is a test image", "image" => "mylovelywife.png", "name" => "i1"}}, path_info: ["api", "image"], path_params: %{}, port: 4000, private: %{ApiAppWeb.Router => {[], %{}}, :phoenix_action => :create, :phoenix_controller => ApiAppWeb.ImageController, :phoenix_endpoint => ApiAppWeb.Endpoint, :phoenix_format => "json", :phoenix_layout => {ApiAppWeb.LayoutView, :app}, :phoenix_router => ApiAppWeb.Router, :phoenix_view => ApiAppWeb.ImageView, :plug_session_fetch => #Function<1.32542428/1 in Plug.Session.fetch_session/1>}, query_params: %{}, query_string: "", remote_ip: {172, 25, 0, 1}, req_cookies: %Plug.Conn.Unfetched{aspect: :cookies}, req_headers: [{"accept", "*/*"}, {"content-length", "114"}, {"content-type", "application/json"}, {"host", "localhost:4000"}, {"user-agent", "curl/7.64.1"}], request_path: "/api/image", resp_body: nil, resp_cookies: %{}, resp_headers: [{"cache-control", "max-age=0, private, must-revalidate"}, {"x-request-id", "FgevKmnwQSUnG-UAAAzR"}], scheme: :http, script_name: [], secret_key_base: :..., state: :unset, status: nil}, {:error, #Ecto.Changeset<action: :insert, changes: %{description: "This is a test image", image: "mylovelywife.png", name: "i1"}, errors: [categories_id: {"can't be blank", [validation: :required]}], data: #ApiApp.Images.Image<>, valid?: false>})
phoenix_1  |         (api_app 0.1.0) lib/api_app_web/controllers/image_controller.ex:1: ApiAppWeb.ImageController.action/2
phoenix_1  |         (api_app 0.1.0) lib/api_app_web/controllers/image_controller.ex:1: ApiAppWeb.ImageController.phoenix_controller_pipeline/2
phoenix_1  |         (phoenix 1.4.16) lib/phoenix/router.ex:288: Phoenix.Router.__call__/2
phoenix_1  |         (api_app 0.1.0) lib/api_app_web/endpoint.ex:1: ApiAppWeb.Endpoint.plug_builder_call/2
phoenix_1  |         (api_app 0.1.0) lib/api_app_web/endpoint.ex:1: ApiAppWeb.Endpoint.call/2
phoenix_1  |         (phoenix 1.4.16) lib/phoenix/endpoint/cowboy2_handler.ex:42: Phoenix.Endpoint.Cowboy2Handler.init/4
phoenix_1  |         (cowboy 2.7.0) /backend/deps/cowboy/src/cowboy_handler.erl:41: :cowboy_handler.execute/2
phoenix_1  |         (cowboy 2.7.0) /backend/deps/cowboy/src/cowboy_stream_h.erl:320: :cowboy_stream_h.execute/3
phoenix_1  |         (cowboy 2.7.0) /backend/deps/cowboy/src/cowboy_stream_h.erl:302: :cowboy_stream_h.request_process/3
phoenix_1  |         (stdlib 3.12) proc_lib.erl:249: :proc_lib.init_p_do_apply/3

Here is the image scheme updated:

defmodule ApiApp.Images.Image do
  use Ecto.Schema
  import Ecto.Changeset

  alias ApiApp.Images.Categories

  schema "image" do
    field :description, :string
    field :image, :string
    field :name, :string
    belongs_to :category, Categories

    timestamps()
  end

  @doc false
  def changeset(image, attrs) do
    image
    |> cast(attrs, [:name, :description, :image, :category_id])
    |> validate_required([:name, :description, :image, :category_id])
    |> foreign_key_constraint(:category_id,
         name: :image_category_id_fkey,
         message: "Category not found!"
       )
  end
end

Even with "categories": {"id": 1}