# `Ash.Resource.Change.CascadeUpdate`
[🔗](https://github.com/ash-project/ash/blob/v3.23.1/lib/ash/resource/change/cascade_update.ex#L5)

Cascade a resource's update action to a related resource's update action.

Adds an after-action hook that explicitly calls update on any records related
via the named relationship.  It will optimise for bulk updates where
possible.

Allows you to copy fields from the arguments or changes to the destination,
this way you can cascade a bunch of changes downstream.

> #### Beware database constraints {: .warning}
>
> Think carefully before using this change with data layers which enforce
> referential integrity (ie PostgreSQL and SQLite) and you may need to defer
> constraints for the relationship in question.
>
> See also:
>   1. [`postgres.references.reference.deferrable` DSL](https://hexdocs.pm/ash_postgres/dsl-ashpostgres-datalayer.html#postgres-references-reference-deferrable)
>   2. [`sqlite.references.reference.deferrable` DSL](https://hexdocs.pm/ash_sqlite/dsl-ashsqlite-datalayer.html#sqlite-references-reference-deferrable)
>   3. [PostgreSQL's `SET CONSTRAINTS` documentation](https://www.postgresql.org/docs/current/sql-set-constraints.html)
>   4. [SQLite's `PRAGMA defer_foreign_keys` documentation](https://www.sqlite.org/pragma.html#pragma_defer_foreign_keys)

> #### Cascading notifications {: .tip}
>
> By default notifications are disabled for the related updates. This is to avoid potentially sending a **lot** of notifications for high-cardinality relationships.

## Options

* `:relationship` (`t:atom/0`) - Required. The name of the relationship to work on

* `:action` (`t:atom/0`) - The name of the update action to call on the related resource. Uses the primary update by default.

* `:copy_inputs` (list of `t:atom/0`) - A list of fields to copy & pass on to the downstream update. The source action cannot be atomic. The default value is `[]`.

* `:read_action` (`t:atom/0`) - The name of the read action to call on the related resource to find results to be updated

* `:return_notifications?` (`t:boolean/0`) - Return notifications for all updated records? The default value is `false`.

## Example

    change {Ash.Resource.Change.CascadeUpdate, relationship: :comments, action: :update_all, copy_inputs: [:name]}

    or, equivalently using `Ash.Resource.Change.Builtins.cascade_update/2`:

    change cascade_update(:comments, action: :update_all, copy_inputs: [:name])

---

*Consult [api-reference.md](api-reference.md) for complete listing*