In a many-to-many relationship, use the attach method to link a child model to its parent. In contrast, for a one-to-one relationship, use the associate method:

use App\Models\Post;

$post = Post::findOrFail(6);

// Associate the post with the user (not yet saved to the database)
$post->user()->associate(auth()->user());

// Save the post along with the relationship
$post->save();

The reverse of the previous method is `disassociate`, which does not remove the user's post but sets the `user_id` to NULL.