我创建了一个聚合管道,它从数据库返回许多文档。我还可以使用“console.log”查看结果。但是当我使用 Postman 时,我无法在响应中返回结果。您可以测试它在 PostMan 上使用 AreaName=Hungary,Resolution=PT15M,Year=2018,Month=1,Day=1
var express = require('express');
var router = express.Router();
var assert = require('assert')
const URL = 'mongodb+srv://user:<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="423731273002212e3731362730726f72323531316c2f2d2c252d26206c2c2736" rel="noreferrer noopener nofollow">[email protected]</a>/test?retryWrites=true&w=majority'
const MongoClient = require('mongodb').MongoClient
//const CircularJSON = require('circular-json');
//const {parse, stringify} = require('flatted/cjs');
router.get('/:AreaName/:Resolution/:Year/:Month/:Day', (req, res, next) => {
const _AreaName=req.params.AreaName
const _Resolution=req.params.Resolution
const _Year = parseInt(req.params.Year)
const _Month = parseInt(req.params.Month)
const _Day = parseInt(req.params.Day)
MongoClient.connect(URL,{
useNewUrlParser: true,
useUnifiedTopology: true},
async (err, client) => {
if (err) throw err;
else console.log('connected to db');
assert.equal(null, err)
const db = client.db('energy')
var collection = db.collection('ActualTotalLoad')
const agg = [
{
$match :
{
AreaName: _AreaName,
Day : _Day,
Month: _Month,
Year: _Year
}
},
{
$lookup:
{
from: 'ResolutionCode',
localField: 'ResolutionCodeId',
foreignField : 'Id',
as: "resolution_codes"
}
},
{
$unwind: {path : "$resolution_codes"}
},
{
$match : {'resolution_codes.ResolutionCodeText' : _Resolution}
},
{
$addFields : {ResolutionCode : '$resolution_codes.ResolutionCodeText',
Source :'entso-e',
Dataset :'ActualTotalLoad'
}
},
{
$project :
{
_id:0,
Id : 1,
ResolutionCodeId:1,
Source : 1,
AreaName: 1,
Year : 1,
Month : 1,
Day : 1,
ResolutionCode : 1
}
}
];
var cursor = collection.aggregate(agg)
cursor.forEach(doc => {
console.log(doc)
})
await cursor.toArray((error, result) => {
if(error) {
return res.status(500).send(error);
}
cursor.forEach(doc => {
res.send(doc)
})
});
})// connection ends here
})
module.exports = router;
-> 上面的代码返回一个 json,然后服务器崩溃
我可以看到结果 "cursor.forEach(doc => { console.log(doc)}) " 在终端中,这似乎工作正常。我要问的是如何以 json 返回响应。像“res.json(cursor) ” 我尝试了一些不同的函数/方法来做但这似乎不起作用。
更新 回答后我尝试了这个
cursor.toArray((error, result) => {
if(error) {
return res.status(500).send(error);
}
cursor.forEach(doc => {
res.send(doc)
})
});
上面的代码用Postman测试时从数据库返回1个json文档。问题是它只返回一个,然后服务器崩溃了。我要返回的文档是多个。错误消息为错误[ERR_HTTP_HEADERS_SENT]:发送到客户端后无法设置 header
最佳答案
您需要调用.toArray()方法返回所有结果。
编辑:调试代码。将 Route
更改为 App
var express = require('express');
var app = express();
var router = express.Router();
var assert = require('assert')
const URL = 'mongodb+srv://user:<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="6e1b1d0b1c2e0d021b1d1a0b1c5e435e1e191d1d4003010009010a0c40000b1a" rel="noreferrer noopener nofollow">[email protected]</a>/test?retryWrites=true&w=majority'
const MongoClient = require('mongodb').MongoClient
//const CircularJSON = require('circular-json');
//const {parse, stringify} = require('flatted/cjs');
app.get('/', function (req, res) {
res.send('Hello World!');
});
app.get('/:AreaName/:Resolution/:Year/:Month/:Day', (req, res) => {
const _AreaName=req.params.AreaName
const _Resolution=req.params.Resolution
const _Year = parseInt(req.params.Year)
const _Month = parseInt(req.params.Month)
const _Day = parseInt(req.params.Day)
MongoClient.connect(URL,{
useNewUrlParser: true,
useUnifiedTopology: true},
async (err, client) => {
if (err) throw err;
else console.log('connected to db');
assert.equal(null, err)
const db = client.db('energy')
var collection = db.collection('ActualTotalLoad')
const agg = [
{
$match :
{
AreaName: _AreaName,
Day : _Day,
Month: _Month,
Year: _Year
}
},
{
$lookup:
{
from: 'ResolutionCode',
localField: 'ResolutionCodeId',
foreignField : 'Id',
as: "resolution_codes"
}
},
{
$unwind: {path : "$resolution_codes"}
},
{
$match : {'resolution_codes.ResolutionCodeText' : _Resolution}
},
{
$addFields : {ResolutionCode : '$resolution_codes.ResolutionCodeText',
Source :'entso-e',
Dataset :'ActualTotalLoad'
}
},
{
$project :
{
_id:0,
Id : 1,
ResolutionCodeId:1,
Source : 1,
AreaName: 1,
Year : 1,
Month : 1,
Day : 1,
ResolutionCode : 1
}
}
];
var cursor = collection.aggregate(agg)
await cursor.toArray((error, result) => {
if(error) {
return res.status(500).send(error);
}
res.send(result);
});
})// connection ends here
})
module.exports = router;
app.listen(3000, function () {
console.log('Example app listening on port 3000!');
});
关于node.js - NodeJS、MongoDB - 从 GET 请求中的聚合返回 JSON 响应,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/59617836/