ecto-nested-associations

Ecto cast_assoc manages nested has_many associations by casting child changesets alongside the parent, ensuring safe creation and updates in one transaction. You must preload associations before updates to avoid silent data loss during list diffs.

Use Ecto.Multi for multi-table transactions when you need explicit rollback control across independent operations. Cast_assoc is better for parent-child updates, while Ecto.Multi chains discrete database operations with reliable atomic rollbacks.

Updating nested Ecto associations without preloading causes silent data loss because Ecto cannot diff existing records against incoming changes. Preloading ensures the current state is loaded so cast_assoc can accurately determine which records to update or delete.

Configure on_replace: :delete in your schema to safely remove items from has_many associations during cast_assoc operations. This ensures Ecto deletes child records that are missing from the incoming changeset data, maintaining referential integrity.

Yes, Ecto cast_embed works with embedded schemas to manage nested data entirely within a single table column. It ensures the correct data shape is validated and persisted without requiring separate database tables for the embedded records.

Reliable Ecto nested association management requires explicit migrations and indexing to maintain data integrity. This includes adding foreign key constraints and database indexes to support safe propagation of changes and prevent orphaned records.