Select input for foreign key field

[netProphET]

A common pattern in admin UIs is to let the user select a foreign key value from a list of options from the related table. For example, when creating or editing an Item, the user might like to pick a Category from a list instead of copy/pasting a Category id from another view.

I've confirmed that this feature does not currently exist in ash_admin.

I have cooked up a naive solution which I'm happy to share via PR, but as I'm new to Ash (as well as Elixir) I suspect I don't have the configuration part well solved, or the feature set for that matter. It feels like with Ash it's important to get this part right first.

An example

In ash_admin:

• I've added a :select field type
• AshAdmin.Components.Resource.Form builds the select options by calling read action named :select_options on the configured module

Then my Resources look like this:

MyProject.Catalog.Item

  admin do
    form do
      field :category_id,
        type: :select,
        options: %{
          module: MyProject.Catalog.Category
        }
    end
  end

MyProject.Catalog.Category

  actions do
    read :select_options do
      prepare build(select: [:id, :name])
    end
  end

Things I'm unsure about:

• having to pass the module name to the AshAdmin.Resource.Field: there's probably a way it could be derived from the relationship, but would that suffice always?
• requiring the developer to add a :select_options read action in the related resource: too heavy handed? Would this be better if it were derived from something?
• adding "options" to the AshAdmin.Resource.Field struct in this way: does it unneccessarily clutter the AshAdmin.Resource.Field module? Is there a better abstraction?
• I can imagine wanting to configure other things such as overriding the field label: In my example we have the "Category Id" field, but in the context of a select box, the user is really choosing a "Category"

I look forward to thoughts on this.

[zachdaniel]

I think that this should likely be derived automatically based on configuration in the destination resource perhaps?

Something like:

• if we are editing a field, and that field is a foreign key, we check if there is a config called like label_field on the destination resource, then we select with that label.
• if we're editing a relationship, we know what the particular destination is, so if what we're modifying is the primary key of the destination resource and the destination has an label_field then we can do the same thing.
• we also make sure to "load" the field that is the label_field, that way we can do this

This allows doing things on your users like

label_field :admin_label

....

calculate :admin_label, :string, expr("#{email} (#{id})")