Ideas/app/Models/Idea.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Idea extends Model
{
    use HasFactory;

    protected $fillable = [
        'content',
        'likes'
    ];

    public function comments()
    {
        return $this->hasMany(Comment::class, "idea_id", "id");
    }
}