由于错误，我面临问题，即
发送后无法设置标头
实际上，我正在查询我的MongoDB。
Test.aggregate([
{$match: {'ownerid': req.body.ownerid}},
{$unwind: '$groupname'},
{$project: {_id:1, groupname :"$groupname",}}
], function(error, data){
if(error) {
console.log(error);
} else {
//It will return Two group id.
for(var i=0; i<data.length; i++){
//These are the variables for my custom function which can update my query on another table
var primaryfilter = {'userid': req.body.ownerid};
var secondaryfilter = { "groupowned" : { 'groupid': data[i]._id, 'groupname': data[i].groupname } };
var activityname = 'Group Owned';
updater(req, res, Test1, primaryfilter, secondaryfilter, activityname);
}
}
});
这一个是我的更新程序功能：
var updater = function(req, res, CollectionName, primaryfilter, secondaryfilter, activityname){
CollectionName.update(primaryfilter, {$push: secondaryfilter}, function(error2, result){
if (error2) {
res.send({"error":"true", "status":"500", "message":"Oops! Some error occurred while updating the "+activityname+" on Post"});
} else {
res.send({"error":"false", "status":"201", "message":"Successfully Updated "+activityname+" on Post"});
}
});
};
实际上，我想从测试集合中获取组ID并更新我的辅助表上的所有这些ID，即Test1 我知道这个错误生成由于循环。任何人建议我如何解决这个问题。任何帮助表示赞赏
答案 0 :(得分：2)
当您尝试为给定请求发送多个响应时，会看到您看到的错误。
您正在使用res.send()来呼叫updater()。并且，您在updater()循环内调用for，这意味着您多次调用它。
因此，您最终会在同一请求中多次调用res.send()。这就是导致你看到错误的原因。每个请求只能拨打res.send()一次。
您可能需要做的是累积所有.update()次调用的结果，然后在完成所有操作后发送一个响应。但是，你必须决定你想要的行为。你想发送什么样的回应？像这样的一系列对象？
{"error":"false", "status":"201", "message":"Successfully Updated "+activityname+" on Post"}
还是其他什么？而且，如果您的某个请求出现错误，您希望响应是什么？
由于这是mongodb，您可能希望使用mongodb内置的promise Promise.all()知道所有.update()调用何时完成。
这是接近它的一种方法：
Test.aggregate([
{$match: {'ownerid': req.body.ownerid}},
{$unwind: '$groupname'},
{$project: {_id:1, groupname :"$groupname",}}
], function(error, data){
if(error) {
console.log(error);
} else {
//It will return Two group id.
let promises = [];
for(var i=0; i<data.length; i++){
//These are the variables for my custom function which can update my query on another table
var primaryfilter = {'userid': req.body.ownerid};
var secondaryfilter = { "groupowned" : { 'groupid': data[i]._id, 'groupname': data[i].groupname } };
var activityname = 'Group Owned';
promises.push(updater(Test1, primaryfilter, secondaryfilter, activityname));
}
Promise.all(promises).then(function(results) {
res.json(results);
}).catch(err => {
console.log(err);
res.sendStatus(500);
})
}
});
function updater(CollectionName, primaryfilter, secondaryfilter, activityname){
return CollectionName.update(primaryfilter, {$push: secondaryfilter}).then(function(result) {
return {"error":"false", "status":"201", "message":"Successfully Updated "+activityname+" on Post"};
}).catch(function(err) {
return {"error":"true", "status":"500", "message":"Oops! Some error occurred while updating the "+activityname+" on Post"};
});
};
答案 1 :(得分：0)
当您尝试向给定请求发送多个响应时，会看到您看到的错误。试试这段代码：
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<style>
.dropdown-submenu {
position: relative;
}
.dropdown-submenu .dropdown-menu {
top: 0;
left: 100%;
margin-top: -1px;
}
</style>
</head>
<body>
<div class="container">
<h2>Multi-Level Dropdowns</h2>
<p>In this example, we have created a .dropdown-submenu class for multi-level dropdowns (see style section above).</p>
<p>Note that we have added jQuery to open the multi-level dropdown on click (see script section below).</p>
<div class="dropdown">
<button class="btn btn-default dropdown-toggle" type="button" data-toggle="dropdown">Tutorials
<span class="caret"></span></button>
<ul class="dropdown-menu">
<li><a tabindex="-1" href="#">HTML</a></li>
<li><a tabindex="-1" href="#">CSS</a></li>
<li class="dropdown-submenu">
<a class="test" tabindex="-1" href="#">New dropdown 1 <span class="caret"></span></a>
<ul class="dropdown-menu">
<li><a tabindex="-1" href="#">2nd level dropdown</a></li>
<li><a tabindex="-1" href="#">2nd level dropdown</a></li>
<li class="dropdown-submenu">
<a class="test" href="#">Another dropdown <span class="caret"></span></a>
<ul class="dropdown-menu">
<li><a href="#">3rd level dropdown</a></li>
<li><a href="#">3rd level dropdown</a></li>
</ul>
</li>
</ul>
</li>
<li class="dropdown-submenu">
<a class="test" tabindex="-1" href="#">New dropdown 2 <span class="caret"></span></a>
<ul class="dropdown-menu">
<li><a tabindex="-1" href="#">2nd level dropdown</a></li>
<li><a tabindex="-1" href="#">2nd level dropdown</a></li>
<li class="dropdown-submenu">
<a class="test" href="#">Another dropdown <span class="caret"></span></a>
<ul class="dropdown-menu">
<li><a href="#">3rd level dropdown</a></li>
<li><a href="#">3rd level dropdown</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
</div>
<script>
$(document).ready(function(){
$('.dropdown-submenu a.test').on("click", function(e){
$(this).next('ul').toggle();
e.stopPropagation();
e.preventDefault();
});
});
</script>
</body>
</html>