ash_postgres/documentation/topics/resources/references.md

References

To configure the behavior of generated foreign keys on a resource, we use the references section.

For example:

references do
  reference :post, on_delete: :delete, on_update: :update, name: "comments_to_posts_fkey"
end

Actions are not used for this behavior {: .warning}

No resource logic is applied with these operations! No authorization rules or validations take place, and no notifications are issued. This operation happens directly in the database.

Nothing vs Restrict

references do
  reference :post, on_delete: :nothing
  # vs
  reference :post, on_delete: :restrict
end

The difference between :nothing and :restrict is subtle and, if you are unsure, choose :nothing (the default behavior). :restrict will prevent the deletion from happening before the end of the database transaction, whereas :nothing allows the transaction to complete before doing so. This allows for things like updating or deleting the destination row and then updating updating or deleting the reference(as long as you are in a transaction). The reason that :nothing still ultimately prevents deletion is because postgres enforces foreign key referential integrity.

On Delete

This option is called on_delete, instead of on_destroy, because it is hooking into the database level deletion, not a destroy action in your resource. See the warning above.