18. Constraints and cascades

Rent does not replace database integrity. The schema and migrations create real foreign keys, unique constraints, and referential actions.

The runnable chapter attempts to create a comment for a missing post and requires the database to reject it. It then deletes a real post and verifies ON DELETE CASCADE removed the dependent comment.

let orphan = client
    .create_comment()
    .post_id(999)
    .author_id(1)
    .save()
    .await;

assert!(orphan.is_err());

client.delete_post_one(&post).exec().await?;
assert_eq!(client.comment().count().await?, 0);

It also creates a recursive parent/child relationship, deletes the parent, and verifies ON DELETE SET NULL detached the child without deleting it.

The foreign keys and referential actions are all visible in crates/rent/examples/tutorial_17_constraints_and_cascades/schema.rsl. Run cargo run -p rent --example tutorial_17_constraints_and_cascades. The same integrity workflow runs under nextest.