Ash Elixir•2y ago

Setting defaults for a form input that is an argument and not an attribute?

I have an update action that takes an argument. In the form for this action, I need to set the default value for the form input. The default value is dependent on the current state of the resource being updated. I explored using the default option for an action argument; however, It accepts a zero-argument function, so there's no way to get the resource being updated. I explored using the prepare_params option for AshPhoenix.Form.for_update but I couldn't find any examples. It's arrity 2 and receives the params but is only called when the form is validated or submitted. Side quest(ion): what's the difference between prepare_params and transform_params if they're both called only on validate and submit?

7 Replies

ZachDaniel•2y ago

IIRC prepare_params is pre-validate and transform_params is post validate oh, no thats wrong transform_params is passed to child forms so all params on all forms go through it

Robert GraffOP•2y ago

How can I set the params before I render the form?

ZachDaniel•2y ago

you could validate it once w/ your own params

Robert GraffOP•2y ago

Just saw prepare_source, trying to figure out how that works.

ZachDaniel•2y ago

so, lets revisit the initial use case though if you have a default value that is based on the current state of things, you can do that with a change on the action as well

change fn changeset, _ -> 
  if changeset.arguments[:foo] do
    changeset
  else
    Ash.Changset.set_argument(changeset, :foo, changeset.data.bar)
  end
end

change fn changeset, _ -> 
  if changeset.arguments[:foo] do
    changeset
  else
    Ash.Changset.set_argument(changeset, :foo, changeset.data.bar)
  end
end

(for example) changes run when we validate the form (which is why anything w/ side effects goes in before/after action hooks)

Robert GraffOP•2y ago

ok, so I can create my input form and then immediately validate it to get the argument set? I got it working with prepare_source.

              AshPhoenix.Form.for_update(plan, :update,
                api: Environments,
                prepare_source: fn changeset ->
                  Ash.Changeset.set_argument(
                    changeset,
                    :feature_keys,
                    default_feature_keys(changeset.data)
                  )
                end
              )

              AshPhoenix.Form.for_update(plan, :update,
                api: Environments,
                prepare_source: fn changeset ->
                  Ash.Changeset.set_argument(
                    changeset,
                    :feature_keys,
                    default_feature_keys(changeset.data)
                  )
                end
              )

I like this a little better because the defaults are more related to the form than the action.

Robert GraffOP•2y ago

Made a few doc changes. Hopefully, my understanding is correct. https://github.com/ash-project/ash_phoenix/pull/97/files

GitHub

Improve form documentation by rgraff · Pull Request #97 · ash-proje...

Improvements to the Form documentation based on my understanding and looking at source code. These very small tweaks would've helped me today. Contributor checklist Bug fixes include regr...

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Setting defaults for a form input that is an argument and not an attribute?

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