Laravel模型不起作用

Question

I'm trying to create post page with comments; however, it's not working when I add the comment to a post because the system doesn't recognize the post id. What I'm I doing wrong that it doesn't know that the post_id is equal to $post_id

I'm getting the following error:

SQLSTATE[HY000]: General error: 1364 Field 'post_id' doesn't have a default value (SQL: insert into comments (body, updated_at, created_at) values (This is a test comment, 2017-08-15 19:51:47, 2017-08-15 19:51:47))

COMMENTS FORM

 <div class="well">
    <h4>Leave a Comment:</h4>

    <form role="form" method="post" action="{{ $post->id }}/comments">
    {{  csrf_field() }}

       <div class="form-group">
          <textarea name="body" class="form-control" rows="3"></textarea>
       </div>

       <button type="submit" class="btn btn-primary">Submit</button>
    </form>
 </div>

ROUTE

Route::post('/posts/{post}/comments', 'CommentController@store');

CONTROLLER

public function store(Post $post)
{
    $post->addComment(request('body'));

    return back();
}

COMMENT MODEL

class Comment extends Model
{
    protected $fillable = ['body'];

    public function post()
    {
        return $this->belongsTo(Post::class);
    }
}

POST MODEL

class Post extends Model
{
    public function addComment($body)
    {
        Comment::create([
            'body' => $body,
            'post_id' => $this->id
        ]);
    }

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

Answer 1

post_id isn't in fillable array:

class Comment extends Model
{
    protected $fillable = ['body', 'post_id']; //<---
    ...
}