模型里面

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    //

   protected $table = "posts";
   public $primaryKey = 'id';

   public function user()
   {
      return $this->belongsTo("App\Models\User","user_id",'id');
   }

   public function comments()
   {
      return $this->hasMany('App\Models\Comment','post_id','id')->orderBy("created_at",'desc');
   }
}

控制器查询列表
$posts = Post::withCount("comments")->orderBy("created_at",'desc')->paginate(6);


视图里面使用

{{ $post->comments_count }}