如何使用 NodeJS 仅将 NeDB 数据库中的某些字段存储到数组中

Question

我有一个嵌入式 NeDB 数据库，其中包含多个条目和多个字段，我只想从每个条目中获取日期并将其存储到一个数组中。我正在使用 NeDB、NodeJS 和 express。

数据集如下所示：

{"goalName":"swim 5km","details":"I want to swim 5km","date":"2021-05-15","completed":false,"author":"somename","_id":"BMnvTm54rNbwc9D4"}
{"goalName":"swim 5km","details":" I want to swim another 5km","date":"2021-03-14","completed":false,"author":"somename","_id":"EwEicEYZAfFxY9Z6"}
{"goalName":"20 pushups","details":"I want to complete 20 full pushups","date":"2021-05-14","completed":false,"author":"anthername","_id":"rP7q6L8jnwGyAgGD"}

我只对作者姓名的日期感兴趣，

我可以使用以下方法检索这些文档：

getEntriesByUser(userName) {
  return new Promise((resolve, reject) => {
    this.db.find({ 'author': userName }, function (err, entries) {
      if (err) {
        reject(err);
      } else {
        resolve(entries);
        console.log('getEntriesByUser returns: ', entries);
      }
    })
  })
}

然后 returns 用户名 = 某个用户名的文档，但我只对日期感兴趣。最好将它们存储到一个数组中，结果如下：

[2021-05-15, 2021-03-14, 2021-05-14]

我怎么会这样做？

感谢您的帮助！

Answer 1

您可以使用 find() 和 findOne() 方法的可选第二个 projection 参数来包含或省略返回记录的属性。参见：NeDB#projections.

db.find({ author: userName }, { date: 1, _id: 0 }, function (err, docs) {...});

const
  Datastore = Nedb,
  db = new Datastore(),
  data = [
    { goalName: "swim 5km", details: "I want to swim 5km", date: "2021-05-15", completed: false, author: "somename" },
    { goalName: "swim 5km", details: " I want to swim another 5km", date: "2021-03-14", completed: false, author: "somename" },
    { goalName: "20 pushups", details: "I want to complete 20 full pushups", date: "2021-05-14", completed: false, author: "anthername" },
  ];

for (const datum of data) {
  db.insert(datum);
}

function getEntriesByUser(userName) {
  return new Promise((resolve, reject) => {
    db.find({ author: userName }, { date: 1, _id: 0 }, function (err, entries) {
      if (err) {
        reject(err);
      } else {
        resolve(entries);
        console.log('getEntriesByUser returns: ', entries);
      }
    })
  })
}

getEntriesByUser('somename').then((entries) => {
  console.log('Mapped return value: ', entries.map(({ date }) => date));
});

.as-console-wrapper { max-height: 100% !important; top: 0; }

<script src="https://cdnjs.cloudflare.com/ajax/libs/nedb/1.8.0/nedb.min.js"></script>

如何使用 NodeJS 仅将 NeDB 数据库中的某些字段存储到数组中

How to store only certain fields from NeDB database into an array with NodeJS

javascript

node.js

express

nedb