feat: Add attribute_always_select? option to belongs_to relationships

[emadshaaban92]

Contributor checklist

Leave anything that you believe does not apply unchecked.

• I accept the AI Policy, or AI was not used in the creation of this PR.
• Bug fixes include regression tests
• Chores
• Documentation changes
• Features include unit/acceptance tests
• Refactoring
• Update dependencies

Problem

When reading records with a limited select, foreign key attributes from belongs_to relationships get masked as Ash.NotLoaded. If you then call an update action on that record, any change with a where [present(:foreign_key)] guard will silently skip — even though the value exists in the database.

Example

Consider a Task resource that optionally belongs to a Project:

belongs_to :project, MyApp.PM.Project, allow_nil?: true

When a task is completed, we want to check if the entire project is now done and update its status — but only for project-linked tasks:

update :complete do
  change transition_state(:completed)

  change MyApp.PM.Task.Changes.AutoCompleteProject do
    where [present(:project_id)]
  end
end

In a dashboard LiveView, tasks are loaded with a limited select for performance:

Task
|> Ash.Query.select([:id, :state, :title, :due_at])
|> Ash.read!()

When a user marks a task as complete, the action runs on the record as-is. Since project_id wasn't in the select, it's Ash.NotLoaded, present? returns false, and the AutoCompleteProject change is silently skipped — even for tasks that do belong to a project.

The current workaround is to either:

• Always remember to include the FK in every query's select (error-prone)
• Define the attribute manually with always_select? true and set define_attribute? false (verbose)

Solution

Adds attribute_always_select? to belongs_to, consistent with existing attribute_writable? and attribute_public? options:

belongs_to :project, MyApp.PM.Project,
  allow_nil?: true,
  attribute_always_select?: true

Alternative / Future Consideration

ensure_loaded or preload on actions

A complementary approach would be an ensure_loaded option that loads specific fields on the record before running validations and changes. Unlike attribute_always_select? (which is attribute-scoped and global), ensure_loaded would generalize to calculations, aggregates, and relationships, and could be scoped to specific actions.

update :complete do
  ensure_loaded [:project_id]

  change transition_state(:completed)

  change MyApp.PM.Task.Changes.AutoCompleteProject do
    where [present(:project_id)]
  end
end

Note: Code in this PR is hand-written. The PR description was generated with AI assistance.

[zachdaniel]

There is an option called action_select which you can use to ensure certain attributes are selected on the base record. Have you tried that? This change is useful anyway though 😄

[zachdaniel]

Please make sure to run mix spark.cheat_sheets locally.