Laravel eloquent获取关系计数

// User模型
class User extends Model
{
    public function phone()
    {
        return $this->hasOne(Phone::class);
    }
}

// 获取用户的电话数量
$count = User::withCount('phone')->find(1)->phone_count;

// Post模型
class Post extends Model
{
    public function comments()
    {
        return $this->hasMany(Comment::class);
    }
}

// 获取文章的评论数量
$count = Post::withCount('comments')->find(1)->comments_count;

// User模型
class User extends Model
{
    public function roles()
    {
        return $this->belongsToMany(Role::class);
    }
}

// 获取用户的角色数量
$count = User::withCount('roles')->find(1)->roles_count;