Avoid This Laravel Enum Trap: Learn How to Fix It Before It Breaks Your Project!

by Savio Resende

Enums are a way to represent a fixed set of values in your application, often tied to specific use cases like statuses, roles, or categories. Laravel allows developers to use type casting with enums to ensure these values are strictly typed when retrieved from the database, making the code cleaner and reducing potential bugs. However, while type casting might initially seem like an organized and efficient solution, it can lead to significant challenges as your software evolves and your codebase grows, especially in legacy systems.

In an ideal software development world, every new task starts fresh. You begin by creating a clean database and then you tailor it to the task at hand, ensuring that your initial dataset is perfectly seeded to reproduce specific scenarios. This allows you to write precise tests to validate those scenarios while covering additional cases as they happen. When new or unique scenarios are required, the process becomes iterative—you intentionally design and implement them with a clear focus.

This approach assumes you’re starting with greenfield projects or maintaining codebases with flawless processes. But in the real world, especially when maintaining legacy code, things aren’t so simple. As software evolves, enums and their use cases change. New cases are added, old cases become deprecated, and business requirements shift over time. Deprecating enum cases introduces complexity. When you deprecate a specific enum case, you might mark it as such in your code, intending to remove it in the future. But if that enum value is persisted in your database, removing it becomes problematic.

Here’s where things get tricky: (1) If you remove the deprecated case from your enum class but it still exists in your database, Laravel's magic type casting in Eloquent models will throw the error "X is not a valid backing value for enum EnumClassY." (2) Debugging becomes a nightmare. Since the error originates from Laravel’s magical type casting, it’s often difficult to trace its source, much like debugging errors in virtualized DOM frameworks in JavaScript. Without prior experience with this specific issue, you might struggle to find a solution.

This happens for 3 reasons:

First, Laravel’s Eloquent models simplify many tasks, but their magic can become a double-edged sword. When enum casting fails, you’re left without a clear stack trace or error source.
Second, even if you’ve deprecated a value in your code, that value may still exist in your database. Deleting data to resolve the issue is often not an option, especially when working with production environments where data integrity is critical. Suddenly, you might see an error that you can’t trace back to its source, and you’re left with a broken system.
Third, imagine deploying a version of your application where a new enum case has been added via a migration. If a bug forces you to roll back to an older version of your codebase that doesn’t yet recognize the new case, you’re in trouble. The old code won’t know how to handle the new enum, causing further errors.

After battling with these issues, here are 2 insights:

Avoid Over-reliance on Enum Casting: while it’s tempting to cast enums directly in your models, remember that doing so ties your database data too tightly to your code.
Making casting intentional by using a custom enum caster is ideal since it allows you to handle errors gracefully. Instead of letting uncaught exceptions occur when trying to use an enum that is deprecated or nonexistent, you can implement logic to report the issue clearly. This approach ensures the system fails in a controlled and debuggable manner, reducing confusion and enabling quicker resolution of problems.

Let’s consider a concrete example to understand how to handle enums in a way that avoids issues. Imagine you’re adding a type column to your users table. This column specifies the type of user, and at a certain point, your requirements define three types: bot, robot, and user. Over time, the requirements evolve: robot type is deprecated. Despite deprecation, some records in your database still reference the robot type, and some business logic relies on its existence. This includes contextual data, like model states, which were influenced by the robot type. Workflows and processes were built around the robot type, and removing it entirely could break your application.

Now, you face a decision: should you remove the robot value from the type column, or handle it differently? Simply deleting the value introduces risks, such as breaking existing business rules or losing historical context. However, leaving it indefinitely can lead to technical debt and confusion. The best approach is a middle ground, leveraging Laravel’s custom casters to handle these scenarios gracefully.

A custom caster allows you to customize how Eloquent models handle type casting, avoiding uncaught exceptions while giving you the flexibility to decide how to handle deprecated or invalid enum values (instead of having to handle with an exception every time you instantiate your users).

In the Listing 1 is my proposal Caster:

<?php  
  
namespace App\Casts;  
  
use App\Enums\UserType;  
use Illuminate\Contracts\Database\Eloquent\CastsAttributes;  
use Illuminate\Database\Eloquent\Model;  
  
class UserTypeCast implements CastsAttributes  
{  
    /**  
     * @param  array<string, mixed>  $attributes  
     */  
    public function get(Model $model, string $key, mixed $value, array $attributes): mixed  
    {  
        return rescue(fn() => UserType::tryFrom($value), report: false);  
    }  
  
    /**  
     * @param  array<string, mixed>  $attributes  
     */  
    public function set(Model $model, string $key, mixed $value, array $attributes): mixed  
    {  
        return $value instanceof UserType ? $value->value : $value;  
    }  
}

Listing 1: Custom Caster for UserType

Takeaways from this strategy:

Graceful Failure: Instead of throwing an uncaught exception, the custom caster logs and reports invalid enum values, enabling you to track issues.
Flexibility: Returning null allows you to decide at runtime how to handle deprecated or missing values without breaking the application.
Maintainability: This approach prevents the accumulation of technical debt by encouraging proactive handling of edge cases and legacy data.
User-side Decisions: By not breaking the application, you enable system users to decide how to handle deprecated values, such as converting to a default type or retiring the record.

Type casting for enums in Laravel can seem like an elegant solution at first glance. But as your application grows, what starts as a helpful feature can quickly turn into a maintenance burden. By understanding the pitfalls and planning for the future, you can avoid getting trapped by past decisions. Remember, experience often teaches us that simplicity and foresight are the keys to robust, maintainable software.