How do Polymorphic Relationships work in Eloquent, and what are the risks of storing class names?

Short answer

They let one model (such as Comment) relate to multiple model types through commentable_id and commentable_type; storing full class names is fragile and should be replaced with a morphMap.

Explanation

With polymorphic relationships, a comment can belong to a Post or a Video. The table stores the object type and its ID. If it stores the full class name, such as App\Models\Post, renaming the class or its directory breaks existing relationships. A robust solution is to register a stable mapping with Relation::morphMap(['post' => Post::class]) in AppServiceProvider.

Code example

Relation::morphMap([
    'post' => \App\Models\Post::class,
    'video' => \App\Models\Video::class,
]);

Common mistakes

• Letting Eloquent store the full namespace path in the database without using morphMap.

Follow-up questions

• What is the N+1 problem in Eloquent queries, and how do you eliminate it with Eager Loading?

Sources

• Laravel docs — Eloquent: Polymorphic Relationships