如何使用NodeJS

问题描述

我有一个嵌入式 NeDB 数据库，其中包含多个包含多个字段的条目，我希望只获取每个条目的日期并将其存储到数组中。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","_id":"EwEicEYZAfFxY9Z6"}
{"goalName":"20 pushups","details":"I want to complete 20 full pushups","date":"2021-05-14","author":"anthername","_id":"rP7q6L8jnwGyAgGD"}

我只对作者是某个名字的日期感兴趣，

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);
      }
    })
  })
}

然后返回用户名 = someusername 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！

解决方法

您可以使用 projection 和 find() 方法的可选第二个 findOne() 参数来包含或省略返回记录的属性。请参阅：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",{ goalName: "20 pushups",details: "I want to complete 20 full pushups",date: "2021-05-14",author: "anthername" },];

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

function getEntriesByUser(userName) {
  return new Promise((resolve,reject) => {
    db.find({ author: userName },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>

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