从 mongodb 个查询结果集中提取字段

Question

如何从节点 js 中的查询响应中提取 json 字段？

我有一个问题：-

const Allposts = await Post.aggregate([pipeline])

所有帖子：-

  {
    _id: 1,
    type: 'A',
    source: 'B',
    status: 'C',
    totalCount: 7,
    createdAt: 2022-04-13T17:12:28.097Z,
    updatedAt: 2022-04-13T17:12:28.097Z,
    __v: 0
  },
 {
    _id: 2,
    type: 'A',
    source: 'B',
    status: 'C',
    totalCount: 7,
    createdAt: 2022-04-13T17:12:28.097Z,
    updatedAt: 2022-04-13T17:12:28.097Z,
    __v: 0
  },
 {
    _id: 3,
    type: 'A',
    source: 'B',
    status: 'C',
    totalCount: 7,
    createdAt: 2022-04-13T17:12:28.097Z,
    updatedAt: 2022-04-13T17:12:28.097Z,
    __v: 0
  }, and so on

我想提取 totalCount 字段并存储它的值该怎么做？

Answer 1

假设 totalCount 值在所有对象中都相同，您可以使用第一个索引提取第一个值

let tc = Allposts[0].totalCount;

let data = [{
    _id: 1,
    type: 'A',
    source: 'B',
    status: 'C',
    totalCount: 7,
    createdAt: '2022 - 04 - 13 T17: 12: 28.097 Z',
    updatedAt: '2022 - 04 - 13 T17: 12: 28.097 Z',
    __v: 0
  },
  {
    _id: 2,
    type: 'A',
    source: 'B',
    status: 'C',
    totalCount: 7,
    createdAt: '2022 - 04 - 13 T17: 12: 28.097 Z',
    updatedAt: '2022 - 04 - 13 T17: 12: 28.097 Z',
    __v: 0
  },
  {
    _id: 3,
    type: 'A',
    source: 'B',
    status: 'C',
    totalCount: 7,
    createdAt: '2022 - 04 - 13 T17: 12: 28.097 Z',
    updatedAt: '2022 - 04 - 13 T17: 12: 28.097 Z',
    __v: 0
  }
]

let tc = data[0].totalCount;

console.log(tc);

Answer 2

如果您只从查询响应中得到 totalCount 字段，您可以在查询中添加 .project() 如下

const Allposts = await Post.aggregate().project("totalCount -_id");

从 mongodb 个查询结果集中提取字段

Extract field from mongodb query result set

javascript

mongodb

node.js

express

mongodb-query