app/Models/ChatMessage.php

<?php

namespace App\Models;

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

class ChatMessage extends Model
{
    use HasFactory;

    protected $fillable = [
        'chat_conversation_id',
        'role',
        'content',
    ];

    public function conversation(): BelongsTo
    {
        return $this->belongsTo(ChatConversation::class, 'chat_conversation_id');
    }
}