Polymorphic Embedded Resources?

Is it possible to have embedded resources be one or more structs for example

defmodule MainResource do
  use AshResource, data_layer: :embedded

  attributes do
    attribute :some_resource, ResourceB || ResourceA
  end

defmodule MainResource do
  use AshResource, data_layer: :embedded

  attributes do
    attribute :some_resource, ResourceB || ResourceA
  end

Thinking either this is not supported or could be done with some sort of custom type?

10 Replies

ZachDaniel•2y ago

You can use the built in Union type attribute :attribute, :union, constraints: [types: …]

ZachDaniel•2y ago

https://ash-hq.org/docs/module/ash/latest/ash-type-union

Ash HQ

Module: Ash.Type.Union

View the documentation for Ash.Type.Union on Ash HQ.

gvanders•2y ago

Awesome thanks! What’s the form interop story with union types?

ZachDaniel•2y ago

Oh, honestly…it’s just not been handled yet You’re probably going to have to roll your own on that front for now

gvandersOP•2y ago

🫡

ZachDaniel•2y ago

You can still iterate over the values using AshPhoenix.Form.value and all that, and you can use AshPhoenix.Form.update_form to do things like add/remove(if it’s a list). If it’s not then this is probably not too difficult

gvandersOP•2y ago

Grabbing the value of the union type returns an Ash.Resource struct. Are you thinking to then feed that in to an additional AshPhoenix.Form.for_update? My first thought was to implement it similar to multi-step forms where changing the tag value changed the nested form , but I haven't made one of those yet so thats all in theory

ZachDaniel•2y ago

🤔 I think you might need to like extract the values yourself instead of using AshPhoenix.Form. Just vanilla form stuff.

Alex Slade•9mo ago

@Zach Daniel sorry to dig up an old post, but what's the lowest-pain way of doing this? I'm trying to do something similar where a resource has an embedded resource which could be 1 of ~5 types. The types are fairly complex (they each represent external API data from a different provider) Will a union type cause more headaches than, say, having 5 attributes; leaving them all nil except for the one that matches the type we want to use. I'm aiming for an easy story for things like validations and form editing.

ZachDaniel•9mo ago

A union is the way to go 👍 AshPhoenix.Form knows how to handle them now

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Polymorphic Embedded Resources?

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