alfredfriedrich
Using a calculate in a form field
Hello,
first time playing around with Ash and hitting a wall. I’m trying to use a calucate in a form field. Lets say I have an attribute :duration, :integer and an attribute :duration_unit, :duration_name in a resource, and a calculate :duration_option, expr(duration <> " " <> duration_unit).
If I try to use the duration_option in a form field, I’m only getting a generic error from AshPhoenix.Form.submit.
I’ve looked at the custom composable types, but I’m using AshSqlite and it does not support this.
I guess “I’m using it wrong”, could someone point me at the “Ash” direction, please? 
Thanks alfred
Marked As Solved
zachdaniel
Calculations are likely not the fit here. You are likely looking for arguments. In your create action:
create :create do
accept [:email_address]
argument :duration_option, :string, allow_nil?: false
change SetDurationAttributes
end
defmodule SetDurationAttributes do
use Ash.Resource.Change
def change(changeset, _opts, _context) do
case parse_duration(changeset.arguments.duration_option) do
{:ok, duration, duration_unit} ->
Ash.Changeset.force_change_attributes(
changeset,
%{duration: duration, duration_unit: duration_unit}
)
{:error, error} ->
Ash.Changeset.add_error(changeset, error)
end
end
end
Also Liked
alfredfriedrich
Okay, I can see the benefits of using arguments and changes now. It encapsulates the parsing and converting logic into the resource (or into a Ash.Resource.Change module) and not into the Form. This is much clearer for me, and the prefered solution.
alfredfriedrich
I read a little more in the Ash Framework book and in chapter 2 they use the transform_params option to the form_to_create_resource call, so I tried it like this:
def mount(_, _, socket) do
form = MyApp.MyDomain.form_to_create_my_resource(
transform_params; fn _form, params, _context ->
parse_duration(params)
end
)
socket = assign(socket, :fom, to_form(form)
{:ok, socket}
end
This works for me as expected, as I understand it, if I’d use argument and change it would work on the Ash.Changeset, but as far as my example goes, working on the params directly is good for me.
I used the calculation too for the <select> form field value by the way.
Thanks again, this was fun playing around with 
I will definitely use this on my next project.
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