laravel-SQLSTATE [HY000]：一般错误：1364 字段“agent_id”没有默认值

由于外键字段我有两个模型（Agent，Post），我无法将用户的主键保存为posts表中的外键。我可以手动插入数据，并与父表链接，但当用户从视图中的表单插入时，它会给我该错误的帮助吗。。提前感谢

Agent

<?php

namespace App\Models;
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Agent extends Model
{
    use HasFactory;
    
    public function posts(){
        return $this->hasMany(Post::class);
    }
}

Post

<?php

namespace App\Models;

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

class Post extends Model
{
    use HasFactory;

    public function user(){
        return $this->belongsTo(Agent::class);
    }
}

这是我在控制器中保存数据的方法

 public function savepost(Request $request){
        $post = new Post ;
        $post->title = $request->title ;
        $post->description = $request->description ;
        $post->type = $request->type;
        $saved = $post->save();
       if($saved){
         return back()->with('success','New post has been added successfuly');
     }else{
         return back()->with('fail' , 'Something went wrong , try again later');
     }
    }