如何使用 NodeJS 仅将 NeDB 数据库中的某些字段存储到数组中

Posted 2023-02-19

【中文标题】如何使用 NodeJS 仅将 NeDB 数据库中的某些字段存储到数组中

【英文标题】：How to store only certain fields from NeDB database into an array with NodeJS

【发布时间】：2021-07-31 09:47:41

【问题描述】：

我有一个嵌入式 NeDB 数据库，其中包含多个具有多个字段的条目，我希望只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]

我该怎么做呢？

感谢您的帮助！

【参考方案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。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));
);

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