2
如果使用.toArray()
,我知道你可以使用db.close()
回调里面,像这样:什么时候使用cursor.forEach()调用db.close()?
db.collection('grades').find(query).toArray(function(err, docs) {
if (err) throw err;
console.dir(docs);
db.close();
});
但是,如果你需要遍历数组了吗?对于1)迭代遍历游标来构造数组,然后2)遍历数组来完成你的工作似乎过分了。所以我在想,使用cursor.forEach()
会很好。
var MongoClient = require('mongodb').MongoClient;
MongoClient.connect('mongodb://localhost:27017/weather', function(err, db) {
if (err) throw err;
var cursor = db
.collection('data')
.find({})
.sort({State: 1, Temperature: -1});
var prevState = '';
var curr;
cursor.forEach(function(doc) {
if (doc.State === prevState) return;
db.collection('data').update(doc, { $set: { month_high: true}});
prevState = doc.State;
});
db.close();
});
然而,这给了我一个错误:
~/code/m101js $ node test.js
/Users/azerner/code/node_modules/mongodb/lib/utils.js:97
process.nextTick(function() { throw err; });
^
TypeError: undefined is not a function
at /Users/azerner/code/node_modules/mongodb/lib/cursor.js:527:15
at handleCallback (/Users/azerner/code/node_modules/mongodb/lib/utils.js:95:12)
at /Users/azerner/code/node_modules/mongodb/lib/cursor.js:493:22
at handleCallback (/Users/azerner/code/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:234:5)
at /Users/azerner/code/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:533:22
at queryCallback (/Users/azerner/code/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:167:20)
at Callbacks.flush (/Users/azerner/code/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:86:7)
at Server.destroy (/Users/azerner/code/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:694:41)
at Server.close (/Users/azerner/code/node_modules/mongodb/lib/server.js:344:17)
at Db.close (/Users/azerner/code/node_modules/mongodb/lib/db.js:273:19)
~/code/m101js $ node test.js
/Users/azerner/code/node_modules/mongodb/lib/utils.js:97
process.nextTick(function() { throw err; });
^
TypeError: undefined is not a function
at /Users/azerner/code/node_modules/mongodb/lib/cursor.js:527:15
at handleCallback (/Users/azerner/code/node_modules/mongodb/lib/utils.js:95:12)
at /Users/azerner/code/node_modules/mongodb/lib/cursor.js:493:22
at handleCallback (/Users/azerner/code/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:234:5)
at /Users/azerner/code/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:533:22
at queryCallback (/Users/azerner/code/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:167:20)
at Callbacks.flush (/Users/azerner/code/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:86:7)
at Server.destroy (/Users/azerner/code/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:694:41)
at Server.close (/Users/azerner/code/node_modules/mongodb/lib/server.js:344:17)
at Db.close (/Users/azerner/code/node_modules/mongodb/lib/db.js:273:19)
~/code/m101js $
这似乎是所有的库代码,我真的不知道如何调试它。但看起来问题出在db.close()
。
- 这是吗?
- 如果是这样,那么我会在哪里放
db.close()
?
你为什么要关闭它? – adeneo
@adeneo我不确定。我实际上正在参加[班级](https://university.mongodb.com/courses/10gen/M101JS/2015_May/syllabus),我不太确定自己在做什么。但除非关闭它是你在这种情况下永远不想做的事情,我的问题依然存在。 –
一般而言,我认为大多数应用程序只会连接一次,并保持连接打开,实际上并不需要关闭每次调用DB的连接。 – adeneo