How to prepend character before username automatically?

I usually just do it like you show. You could also create a custom accessor in the user model, like getMentionNameAttribute() where it just returns '@' . $this->username;

Then you could just do

<a href="{{ $user->mentionName }}</a>

https://laravel.com/docs/5.6/eloquent-mutators#accessors-and-mutators

Thanks, @Cronix

Is this correct as I'm getting Undefined property: App\User::$username?

    public function getUsernameAttribute()
    {
        return '@' . $this->username;
    }

I wouldn't do that to username (getUsernameAttribute()). Then everytime you call $user->username it will add the @. I'm sure you want it added sometimes, but not all of the time. That's why I put it in mentionName, so you could still use username.

Is username an actual field in the database for a user? I only used it because you used it in your original post.

Yes, username is an actual field.

I wouldn't do that to username (getUsernameAttribute()). Then everytime you call $user->username it will add the @.

You're right. I'll use another name.

@yansusanto when your problem solved mark it as solved question because it will help others to not look toward unsolved questions. thanks :)