如何在 Node.js 中聚合 MongoDB
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How to MongoDB aggregation in Node.js
提问by user3664775
var mongoose = require('mongoose');
var membersModel = require('./model_member.js');
exports.request_friend_list = function(req, res){
var userid=req.body.userid;
console.log(userid);
// membersModel.find({_id: userid,friends:{status:0}},{_id:0,'friends':1,},function(err,data)
membersModel.aggregate(
{$match: {_id:userid}},
{$project: {friends: 1}},
{$unwind: "$friends"},
{$match: {"friends.status": 0}}
,function(err,data){
if(err){
res.json({status:"error"});
throw err;
}else{
if(JSON.stringify(data).length > 0){
console.log(JSON.stringify(data));
res.json(data);
}
else{
res.json({status: "Data is not Exist."});
console.log("Data is not Exist.");
}
}
});
membersModel.find({...})is operating normally, but memberModel.Aggregation({...})is not working. This also works in MongoDB:
membersModel.find({...})运行正常，但memberModel.Aggregation({...})不工作。这也适用于 MongoDB：
db.members.aggregate({$match:_id: ObjectId("532b4729592f81596d000001"),$project:"friends":1,$unwind:"$friends",$match:"friends.status": 0})
What is the problem?
问题是什么？
回答by Neil Lunn
The likely problem here is that your useridvalue is not actually a correct ObjectIDtype when it is being passed into the pipeline. This results in nothing being "matched" in the initial stage.
这里可能的问题是，当您的userid值ObjectID被传递到管道时，它实际上并不是正确的类型。这导致在初始阶段没有任何“匹配”。
Therefore as a more complete example:
因此，作为一个更完整的例子：
var mongoose = require("mongoose");
var Schema = mongoose.Schema;
var ObjectID = require("mongodb").ObjectID;
mongoose.connect("mongodb://localhost/test");
friendSchema = new Schema({
"name": String,
"status": Number
});
memberSchema = new Schema({
friends: [friendSchema]
});
var Member = mongoose.model("Members", memberSchema );
var userid = new ObjectID("537ec520e98bcb378e811d54");
console.log( userid );
Member.aggregate([
{ "$match": { "_id": userid } },
{ "$unwind": "$friends" },
{ "$match": { "friends.status": 0 } }],
function( err, data ) {
if ( err )
throw err;
console.log( JSON.stringify( data, undefined, 2 ) );
}
);
Which then will match data as expected:
然后将按预期匹配数据：
[
{
"_id": "537ec520e98bcb378e811d54",
"friends": [{
"name": "Ted",
"status": 0
}]
}
]
So be careful to make sure this is of the correct type. The aggregate method does not automatically wrap a string value such as "537ec520e98bcb378e811d54" into an ObjectIDtype when it is mentioned in a pipeline stage against _idin the way that Mongoose does this with other find and update methods.
所以要小心确保这是正确的类型。ObjectID当在管道阶段提及时，聚合方法不会自动将字符串值（例如“537ec520e98bcb378e811d54”）包装成一种类型_id，而 Mongoose 使用其他查找和更新方法执行此操作的方式。
