Validating a multi-column unique key in Laravel Nova

If you're working with Laravel, Nova is a pretty solid CMS option. It offers a lot of control, and you can leverage all the power Laravel and its community have to offer. The solution in this article is no exception: by combining build-in Laravel concepts we can quickly solve our problem.

Validating uniqueness in Nova is no problem. When you install Nova you get a User resource for free, which already includes the right validation rules:

Text::make('Email')
    ->sortable()
    ->rules('required', 'email', 'max:254')
    ->creationRules('unique:users,email')
    ->updateRules('unique:users,email,{{resourceId}}'),

This will produce a neat error message whenever a duplicate email address is being submitted:

However, what do you do when your unique key is made up of multiple columns?

Dealing with multiple columns

To set the stage, imagine a Page resource. Every page has a slug, and a parent_id. Every page’s URL is determined by its slug, preceded by the slugs of its parent.

In other words, the page “Web development”, which is a child of “Services”, which is a child of “About Us”, will end up with the URL: /about-us/services/web-development.

From these rules we can derive a natural constraint. The slug needs to be unique at the level of its parent. A slug may appear multiple times, so long as their parent pages are different.

First, let’s create a migration to generate the correct table:

Schema::create('pages', function (Blueprint $table) {
    $table->id();
    $table->string('title');
    $table->string('slug')->nullable();
});

// Adding a foreign key to the same table
// while creating it is not possible.
Schema::table('pages', function (Blueprint $table) {
    $table
        ->foreignId('parent_id')
        ->nullable()
        ->references('id')
        ->on('pages');

    // Create compound unique index on parent_id and slug:
    // slugs can only exist once at the same level.
    $table->unique(['parent_id', 'slug']);
});

Then we need two fields on the resource, one for slug, one for the parent:

Slug::make('slug')
    ->from('title')
    ->default(''),

BelongsTo::make(
    'parent',
    'parent',
    static::class
)
    ->nullable()
    ->display('title'),

Note that we cannot add unique rules to these fields, because we cannot encapsulate the full rule.

Although Laravel does support unique validation using multiple columns, we have no way of setting the extra value in the context of a Nova Resource.

An example of a rule that would work in theory is this:

Slug::make('slug')
    ->from('title')
    ->default('')
    ->rules('unique:pages,slug,{{resourceId}},id,parent_id,???')

But as you can see, we cannot offer the value for parent_id, because that value won’t exist until after the form is submitted.

Using Nova’s afterValidation hook

In a Nova resource class, you can implement the afterValidation method to do additional validation. The perfect place to add your custom domain logic.

protected static function afterValidation(
    NovaRequest $request,
    $validator
) {
    if ($this->somethingElseIsInvalid()) {
        $validator->errors()->add(
            'field',
            'Something is wrong with this field!'
        );
    }
}

As you can see, you can implement this however you want, and add custom errors to the Validator instance in case of failure.

Here’s the full solution if you’re just here to copy and paste:

protected static function afterValidation(
    NovaRequest $request,
    $validator
) {
    $parentId = $request->post('parent');
    $unique = Rule::unique('pages', 'slug')->where(
        'parent_id',
        $parentId
    );
    if ($request->route('resourceId')) {
        $unique->ignore($request->route('resourceId'));
    }

    $uniqueValidator = Validator::make($request->only('slug'), [
        'slug' => [$unique],
    ]);

    if ($uniqueValidator->fails()) {
        $validator
            ->errors()
            ->add(
                'slug',
                'This slug is already taken on this level.'
            );
    }
}

Let me break it down so you know what’s happening:

$parentId = $request->post('parent');
$unique = Rule::unique('pages', 'slug')->where(
    'parent_id',
    $parentId
);

First, we take the value for parent from the request’s postdata. This is the value that was just submitted in the form.

From this, we create a new unique Rule. The where clause will be tacked on to the query.

if ($request->route('resourceId')) {
    $unique->ignore($request->route('resourceId'));
}

This handles the update case. If we were to omit these lines, no resource could ever be updated again with the same slug, since the rule would always find a matching record: itself!

With the rule in place, we can create new Validator instance, and validate the slug using our custom rule:

$uniqueValidator = Validator::make($request->only('slug'), [
    'slug' => [$unique],
]);

if ($uniqueValidator->fails()) {
    $validator
        ->errors()
        ->add(
            'slug',
            'This slug is already taken on this level.'
        );
}

That’s it! Using a couple of powerful, native, Laravel concepts we can extend Nova’s build-in features to accommodate our own domain rules.

💡 Looking for validating multiple unique columns outside of a Nova context? Read this article to learn more.

📖 Read Laravel Nova’s validation docs.