AshPhoenix.Form.submit is triggering change function to run twice

Say I have a custom change module, like so:

defmodule MyApp.Accounts.Changes.MyCoolChange do
  use Ash.Resource.Change

  @impl true
  def init(opts) do
    {:ok, opts}
  end

  @impl true
  def change(changeset, _opts, _context) do
    dbg("my cool change")
    changeset
  end
end

defmodule MyApp.Accounts.Changes.MyCoolChange do
  use Ash.Resource.Change

  @impl true
  def init(opts) do
    {:ok, opts}
  end

  @impl true
  def change(changeset, _opts, _context) do
    dbg("my cool change")
    changeset
  end
end

When I run this in the iex terminal, the dbg statement only gets output once. That's what I would expect. Now, when I use it in form using AshPhoenix.Form, I get the dbg statement two times when doing Form.submit. I even took out all other code so this was the only thing running. The mount would look like this:

def mount(socket)
  socket =
    socket
    |> assign(form: to_form(MyApp.Domain.to_form_my_action())

  {:noreply, socket}

def mount(socket)
  socket =
    socket
    |> assign(form: to_form(MyApp.Domain.to_form_my_action())

  {:noreply, socket}

Inside the my_action action, it would look like this:

actions do
  create :my_action do
    argument :my_arg, :string, allow_nil?: false
    change MyCoolChange
  end
end

actions do
  create :my_action do
    argument :my_arg, :string, allow_nil?: false
    change MyCoolChange
  end
end

Then the event handler looks like this:

def handle_event("submit", %{"form" => form_data}, socket) do
  case Form.submit(socket.assigns.form, params: form_data}) do
    {:ok, result} ->
      # ...

    {:error, form} ->
      # ...
  end
end

def handle_event("submit", %{"form" => form_data}, socket) do
  case Form.submit(socket.assigns.form, params: form_data}) do
    {:ok, result} ->
      # ...

    {:error, form} ->
      # ...
  end
end

With all this in place, the dbg message at the start ("my cool change") ends up being called two times. I can put a dbg in the handle_event and it's only called once. I've checked everywhere along the path and it's during the Form.submit call that it happens two times. Is that expected behavior or a bug? If I debug inside something like a before_action that is defined in that same change module, the before_action debug only gets called once, same with action_action. But any code inside that change function at the root gets run two times.

7 Replies

ZachDaniel•6mo ago

This is by design 😄 the body of changes are meant to be for cheap setup that can run validations on keypress and hooks are designed to schedule logic for when the action is actually run

SteveOP•6mo ago

Ah, so anything else should be done in those hooks like before_action and after_action then?

ZachDaniel•6mo ago

Yep! Any side effects, or especially slow work etc.

SteveOP•6mo ago

I was going crazy trying to figure out what was going on. It took a while to track it down hahah. I assume even though that change function is run twice, it doesn't seem to queue the hooks more than once, right?

Elixord•6mo ago

Hexdocs Search Results

Searched ash-3.5.21 for multi-step

ash-3.5.21 | extras

Example 3: Complex Workflow with External Services Multi-Step Actions

ZachDaniel•6mo ago

Correct The form discards and rebuilds the underlying changeset each time So its a fresh changeset w/ no hooks each time, and so hooks don't get doubled up etc. That guide I linked has some useful info on hooks, how they work and why etc.

SteveOP•6mo ago

All right, I feel much better now knowing this. Thanks very much!

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AshPhoenix.Form.submit is triggering change function to run twice

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