Ability to use custom indexes for resource identites

[lcmen]

Another question that came to my mind while I was reading a section about "identities" in "Ash Framework" book :)

I would like to make sure that albums are unique based on artist_id and LOWER(name) columns. I defined a following custom_index for the Album resource:

custom_indexes do
  index ["artist_id", "LOWER(name)"],
    name: "albums_unique_name_per_artist_index",
    unique: true
end

Can I reference that index for the identity instead of defining a separate index there? For example, something like this (sudo code that does not work):

identities do
  identity :unique_name_per_artist, index_name: "albums_unique_name_per_artist_index"
end

Thanks!

[zachdaniel]

You can do this slightly more indirectly using identities and calculations_to_sql

calculate :lowercase_name, :string, expr(string_downcase(name))

and then you add it to an identity like so:

identity :unique_name_per_artist, [:artist_id, :lowercase_name]

and then if you do mix ash.codegen, ash_postgres will yell at you instructing you to define a calculations_to_sql definition for that calculation

postgres do
  calculations_to_sql [lowercase_name: "LOWER(name)"]
end

Someday, ash will automatically do that calculations_to_sql bit 😄

[lcmen]

Thank you @zachdaniel ! It works beautfily.

Last question about displaying errors from identities on Phoenix form.

I used following identities and calculations:

postgres do
  table "albums"

  references do
    reference :artist, on_delete: :delete
  end

  repo Tunez.Repo

  calculations_to_sql lowercase_name: "LOWER(name)"
end

calculations do
  calculate :lowercase_name, :string, expr(string_downcase(name))
end

identities do
  identity :unique_name_per_artist, [:lowercase_name, :artist_id], message: "already exists"
end

How can I display "already exists" error message next to name field on the Phoenix form?
With identity :unique_name_per_artist, [:name, :artist_id], message: "already exists" it works automatically as name in the validation matches the field on the form. Is there a way to specify which attribute the calculation is linked to?

[zachdaniel]

There actually is not a way to do it just w/ config in the identity currently 😢. It has been asked about before, but this makes the need a bit clearer. Could you open a proposal?

In the meantime, you would need to use the transform_errors option on AshPhoenix.Form to intercept that specific error and modify it's fields.