假设有三张表：

User: _id, name. 用户

Article: _id, title, content, userId 文章

Comment: _id, articleId, content, userId 评论

如何查询出某个用户发表的所有文章，返回格式如下：

[
  {
    _id: '',
    title: '',
    content: '',
    userId: '',
    userInfo: {
      _id: '',
      name: ''
    } ,
    comments: [{
      _id: '',
      content: '',
      userId: '',
      userInfo: {
        _id: '',
        name: ''
      }
    },{
     ...
    }]
  },
  ...
]