Data Integrity At Two Layers

_posts/2023-05-02-data-integrity-at-two-layers.md

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+---
+title: "Data Integrity At Two Layers"
+date: 2023-05-02
+tags: Laravel, database, mysql
+---
+
+My team loves to enforce type/value integrity at not only the application layer, but also the database layer.
+
+Within the application layer, we rely heavily on [Backed Enums](https://www.php.net/manual/en/language.enumerations.backed.php). They raise a ValueError if there is no matching case. As a bonus, a [column can be cast to an enum easily within Laravel models](https://laravel.com/docs/10.x/eloquent-mutators#enum-casting).
+
+But what about the at the database level?  We rely on foreign key constraints.
+
+Say we have a table called `roles`. 
+
+```sql
+CREATE TABLE `roles` (
+  `id` smallint unsigned NOT NULL AUTO_INCREMENT,
+  `name` varchar(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
+  PRIMARY KEY (`id`),
+  KEY `role_name_index` (`name`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+```
+
+We can associate a user with their hobbies in a `user_hobbies` table.
+
+```sql
+CREATE TABLE `users` (
+  `id` bigint unsigned NOT NULL AUTO_INCREMENT,
+  `name` varchar(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
+  `email` varchar(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
+  `role_id` smallint unsigned NOT NULL,
+  PRIMARY KEY (`id`),
+  KEY `users_role_id_index` (`role_id`),
+  CONSTRAINT `users_role_id_foreign` FOREIGN KEY (`role_id`) REFERENCES `roles` (`id`) ON DELETE CASCADE,
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+```
+