finance_app/app/Models/InvestmentHolding.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class InvestmentHolding extends Model
{
    protected $fillable = [
        'account_id',
        'type',
        'symbol',
        'name',
        'shares',
        'avg_cost',
    ];

    public function account()
    {
        return $this->belongsTo(Account::class);
    }

    public function transactions()
    {
        return $this->hasMany(InvestmentTransaction::class, 'holding_id');
    }

    public function security()
    {
        return $this->hasOne(Security::class, 'code', 'symbol');
    }
}