从MongoDB查询结果集提取字段

Question

如何从节点JS中的查询响应中提取JSON字段？

我有一个查询： -

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

AllPosts： -

  {
    _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字段并存储其值如何？

Answer 1

假设totalCount值在所有对象中都相同，则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

如果仅从查询响应中获得totalCount字段，则可以在查询中添加.project（）如下

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