select input for relationship via label_field config on destination resource POC (#209)

[netProphET]

Addition of a label_field in a destination resource configuration signals to use a select box to represent the related resource.

admin do
    label_field :admin_label
end

label_field can be a resource attribute or a calculation.

Contributor checklist

• [ ] Bug fixes include regression tests
• [ ] Features include unit/acceptance tests

[netProphET]

Revised approach based on feedback to Issue #209

If I'm on the right track, I'll continue with tests and anything else that needs tidying up or documenting. I'm still a bit new to the ecosystem, so guidance is appreciated.

[zachdaniel]

Exciting! I'll look either this weekend or on Monday 🥳

[zachdaniel]

So, this is very cool, but I do worry that it can only really be used for low cardinality relationships. i.e if you had 100k users, you would need a type-ahead that would do things like fetch data after a few characters were displayed etc.

If we add this and someone misuses it, it might look good in dev but then when running in prod it could cause significant issues.

[zachdaniel]

Would you be open to making it a typeahead? It doesn't have to look beautiful :)

[netProphET]

Yeah that concern crossed my mind as well, and a typeahead could be a good solution. Definitely don't want to provide the rope to hang a production site with. However, not sure I love typeahead for the really low cardinality relationships, e.g. say you have 3 Categories to pick from. I'm happy to play around with this till we have something that will scale.

[zachdaniel]

I think it would make sense to do one of two things:

1. fetch some limited number of results, and if there are less than that that come back, we show a select, and if there are more we show a typeahead.
2. make it configurable from the outset in the source form. Like configuring it from the source.

[netProphET]

@zachdaniel this is coming together nicely, but I'm having difficulty with, of all things, the query for typeahead suggestions

This is the current non-working state of my function

  defp fetch_suggestions(resource, query) do
    label_field = AshAdmin.Resource.label_field(resource)
    pk_field = Ash.Resource.Info.primary_key(resource)

    resource
    |> Ash.Query.new()
    |> Ash.Query.load([pk_field, label_field])
    |> Ash.Query.filter(
      contains(
        ^label_field,
        ^%Ash.CiString{string: query}
      )
    )
    |> Ash.read!()
    |> Enum.map(&{Map.get(&1, label_field), &1.id})
  end

I can't seem to make the field name in the contains function dynamic. It works as expected if I replace ^label_field with an actual field name. I'm not sure if I should be turning to a custom action here, or if I'm just missing some syntax with the current approach. Any insight is appreciated.

[zachdaniel]

label_field should be ^ref(label_field)

[netProphET]

Excellent! Thanks. Guess I should rtfm some more ;-)