Nedb更新添加新記錄，而不是更新現有的一個

Question

我真的很苦惱，所以我希望有人可以幫助我理解爲什麼我得到這種行爲。

我在它與以下記錄的文件

{"Id":"","documentPath":"mission.pdf","dName":"BIOLOGY TEST 1110","dCourseNumber":"1110","dSubject":"BIOL","dTerm":"201690","dTitle":"BIOLOGY TEST 1110","student":"491502","timestamp":1486152313972,"assessed":true,"errorCmt":"","uploadDate":"2/3/2017 14:5","_id":"QwKHQ8sRQdivRJDp"} 
{"Id":"","documentPath":"university.pdf","dName":"BIOLOGY TEST 1111","dCourseNumber":"1111","dSubject":"BIOL","dTerm":"201690","dTitle":"BIOLOGY TEST 1111","student":"491502","timestamp":1486151521825,"assessed":false,"errorCmt":"","uploadDate":"2/3/2017 13:52","_id":"mh0pdGERB6fZU4s3"} 

我testdb.js

文件我有：

var Datastore = require('nedb'); 
var db = new Datastore({filename: './db.db', autoload: true}); 

db.update({ _id: "QwKHQ8sRQdivRJDp"}, { $set: { assessed: true} }, {}, function (err, numReplaced) { 
    console.log("replaced---->" + numReplaced); 
}); 

db.find({}).exec(function (err, docs) {console.log(docs);}); 

我在最後執行查找表明，我已經更新一個單獨的記錄並打印出記錄，他們看起來像我期望的那樣。如果我打開db.db我現在看到這一點：

{"Id":"","documentPath":"mission.pdf","dName":"BIOLOGY TEST 1110","dCourseNumber":"1110","dSubject":"BIOL","dTerm":"201690","dTitle":"BIOLOGY TEST 1110","student":"491502","timestamp":1486152313972,"assessed":true,"errorCmt":"","uploadDate":"2/3/2017 14:5","_id":"QwKHQ8sRQdivRJDp"} 
{"Id":"","documentPath":"university.pdf","dName":"BIOLOGY TEST 1111","dCourseNumber":"1111","dSubject":"BIOL","dTerm":"201690","dTitle":"BIOLOGY TEST 1111","student":"491502","timestamp":1486151521825,"assessed":false,"errorCmt":"","uploadDate":"2/3/2017 13:52","_id":"mh0pdGERB6fZU4s3"} 
{"Id":"","documentPath":"mission.pdf","dName":"BIOLOGY TEST 1110","dCourseNumber":"1110","dSubject":"BIOL","dTerm":"201690","dTitle":"BIOLOGY TEST 1110","student":"491502","timestamp":1486152313972,"assessed":true,"errorCmt":"","uploadDate":"2/3/2017 14:5","_id":"QwKHQ8sRQdivRJDp"} 

任何想法，爲什麼我的記錄與新值複製，而不是剛剛更新？

Answer 1

所以事實證明這是在文檔中解釋。

在底層，NeDB的持久性使用append-only格式，這意味着出於性能原因，所有更新和刪除實際上都會在數據文件末尾添加行。

Answer 2

return this.db.update({ _id: "QwKHQ8sRQdivRJDp"}, { $set: { assessed: true} }, function (err, numReplaced) { 
    if (err) { 
     console.log("error---->" + err); 
    } else { 
     console.log("replaced---->" + numReplaced); 
    } 
}); 

，如果你想真正的「更新」和「刪除」，你應該壓縮您的數據庫，請參閱此相關的問題我相信這explenation讓你試試這個

Answer 3

NeBD只使用追加-性能行話瞭解更多關於Nedb的信息 - nedb method update and delete creates a new entry instead updating existing one