Guarded Struct Ash

Ash integration

Reference: usage-rules/ash.md.

Resource template

defmodule MyApp.User do
  use Ash.Resource,
    domain: MyApp.Domain,
    extensions: [GuardedStruct.AshResource]

  guardedstruct do
    auto_wire true   # injects GuardedStruct.AshResource.Change automatically
    field :email, :string, derives: "sanitize(trim, downcase) validate(email_r)"
  end

  attributes do
    uuid_primary_key :id
    attribute :email, :string, allow_nil?: false, public?: true
  end

  actions do
    defaults [:read, :destroy, :create]
    update :update, accept: [:email]
  end
end

auto_wire: false (default) requires a manual changes do change GuardedStruct.AshResource.Change end block.

Atomic mode — three behaviours

Change.atomic/3 inspects every key in changeset.attributes and changeset.atomics. For each owned field (in __guarded_field_name_set__/0):

Non-owned keys are passed through untouched — expr(now()) on a plain Ash attribute (not in guardedstruct) stays atomic.

Three options when an atomic expression is needed

• Accept the fallback — declare a companion action with require_atomic? false. atomic/3 bails, Ash runs change/3 imperatively, update still succeeds.
• Pass a plain value — compute in Elixir, pass via attributes. Stays atomic, pipeline validates.
• Move the field outside guardedstruct — atomic_update(_, expr(... + 1)) works without going through our pipeline.

Bulk

• Ash.bulk_create/3 → uses batch_change/3 (per-row pipeline).
• Ash.bulk_update/3 with strategy: :atomic (default) → uses atomic/3.
• Ash.bulk_update/3 with strategy: :stream → uses change/3.

All three produce identical sanitized results.

Auto-map cascade

__guarded_change__/1 returns plain maps at every depth for nested sub_fields — never structs. This matches Ash's :map attribute type so output drops directly into changeset.attributes without conversion. Set via a process-local flag at the top of validate/3; concurrency-safe.

Don'ts

• Don't add require_atomic? false to every update action — most updates are atomic-safe by default with this extension. Only add it on actions that need to accept Ash.Expr values for owned fields.
• Don't write defstruct or builder/1 in the resource module — Ash provides both. The extension only adds __guarded_change__/1 and metadata.
• Don't rely on function_exported?(MyResource, :__guarded_field_name_set__, 0) — it's always defined on resources using this extension.

Companion modules

• GuardedStruct.AshResource.Info — Ash-flavoured introspection (fields/1, field/2, validate/2, etc.).
• GuardedStruct.AshResource.Change — the bridge change module.