Laravel Polymorphic Relations commentable_type validation

Question

I'm using a REST API to receive the data.
The data model is polymorphic related, similar to the one on the documentation:
https://laravel.com/docs/5.4/eloquent-relationships#polymorphic-relations

posts
    id - integer
    title - string
    body - text

videos
    id - integer
    title - string
    url - string

comments
    id - integer
    body - text
    commentable_id - integer
    commentable_type - string

Let's say, for example, the API is receiving this new comment:

{
    "body": "This a test comment",
    "commentable_type": "posts",
    "commentable_id": "1"
}

How can I validate if the received commentable_type exists and is valid?

Answer 1

If I correctly understand your question, you are trying to validate that the object of the polymorphic relation exists, for the given commentable_type and commentable_id.

If that is the case, there is no existing validation rule to do so, but you can create one.
Based on the documentation, here is what you could do:

First, add the new rule in the boot method of a service provider (e.g. AppServiceProvider):

Validator::extend('poly_exists', function ($attribute, $value, $parameters, $validator) {
    if (!$objectType = array_get($validator->getData(), $parameters[0], false)) {
        return false;
    }

    return !empty(resolve($objectType)->find($value));
});

And this is how you would use it:

'commentable_id' => 'required|poly_exists:commentable_type

What the rule does is it tries and fetches the commentable type from the input values (based on the parameter passed on to the rule, i.e. commentable_type in our case), and then resolves the object and tries to find a record for the given ID ($value).

Please note that for this to work however, the value of commentable_type must be the fully qualified class name (e.g. App\Models\Post).

Hope this helps!

Answer 2

Better approach that includes morphs map:

    Validator::extend('poly_exists', function ($attribute, $value, $parameters, $validator) {
        if (! $type = array_get($validator->getData(), $parameters[0], false)) {
            return false;
        }

        if (Relation::getMorphedModel($type)) {
            $type = Relation::getMorphedModel($type);
        }

        if (! class_exists($type)) {
            return false;
        }

        return ! empty(resolve($type)->find($value));
    });