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Mongodb - watch changestream in documents with nested array element of certain value

Here is my document:
{
"_id": {
"$oid": "6257a55d04bf2167733f5b72"
},
"attributes": {
"CustomerName": "John",
"CustomerID": "28374",
"LoanID": "82349327409234"
"type": "Record",
"Pointers": [
{"type":"car","token_id":"123"},
{"type":"house","token_id":"456"}
]
}
}
Here is my watch query aiming to watch for Pointers elements with type:"car":
var watchCursor = db.loans.watch([
{
$match: {
"$or": [
{
"updateDescription.updatedFields.attributes.Pointers": {
$elemMatch: {
"type": "car"
}
}
},
{
"fullDocument.attributes.Pointers": {
$elemMatch: {
"type": "car"
}
}
}
]
}
}
]);
while (!watchCursor.isExhausted()){
if (watchCursor.hasNext()){
print(JSON.stringify(watchCursor.next()));
}
}
The problem is that I alter the document but it does not return any change results.
As a test, I changed the $elemMatch stage to $exists: true, then alter the document and it returned the changed document successfully.
what's wrong?!

how to find array element using auto generated id in mongodb

currently, I am struggling with how the MongoDB document system works. I want to fetch array elements with an auto-generated id but how to fetch that specific data that I don't know.
my current schema is
const ItemPricesSchema = new mongoose.Schema({
_id : {
type: String
},
ItemsPrices: {
type: [{
barcode : {
type: String
},
itemName : {
type: String
},
price : {
type: String
}
}]
}
});
current data is stored in this way
{
"_id": "sha#c.c",
"ItemsPrices": [
{
"barcode": "345345",
"itemName": "maggie",
"price": "45",
"_id": "620a971e11120abbde5f4c3a"
},
{
"barcode": "356345",
"itemName": "monster",
"price": "70",
"_id": "620a971e11120abbde5f4c3b"
}
],
"__v": 0
}
what I want to achieve is that I want to find array elements through ids
if I want a specific array element with id "620a971e11120abbde5f4c3b" what should I do??
I have tried $unwind , $in, $match...
the result should be like
{
"_id": "sha#c.c",
"ItemsPrices": [
{
"barcode": "356345",
"itemName": "monster",
"price": "70",
"_id": "620a971e11120abbde5f4c3b"
}
],
"__v": 0
}
what I tried is like this from the answer
router.get('/filter/:id', async (req, res) => {
try {
const item = await ItemPricesSchema.aggregate([
{$project: {
"ItemsPrices": {
$filter: {
input: "$ItemsPrices",
as: "item",
cond: {
$eq: [
"$$item._id",
"620a8dd1c88ae3eb88a8107a"
]
}
}
}
}
}
])
res.json(item);
console.log(item);
} catch (error) {
res.status(500).json({message: error.message});
}
})
and returns something like this (Empty arrays)
[
{
"_id": "xvz#zyx.z",
"ItemsPrices": []
},
{
"_id": "zxc#xc.czx",
"ItemsPrices: []
},
{
"_id": "asd#asd.asd",
"ItemsPrices": []
},
{
"_id": "qwe#qwe.qwe",
"ItemsPrices": []
}
]
but If I search for price $$item.price
cond: {
$eq: [
"$$item.price",
"30"
]
}
it returns the perfect output
[
{
"_id": "xvz#zyx.z",
"ItemsPrices": []
},
{
"_id": "zxc#xc.czx",
"ItemsPrices: []
},
{
"_id": "asd#asd.asd",
"ItemsPrices": []
},
{
"_id": "qwe#qwe.qwe",
"ItemsPrices": [
{
"barcode":"234456345",
"price":"30",
"itemName":"monster",
"_id":"620a8dd1c88ae3eb88a8107a"
}
]
}
]

You can do an aggregation with $project and apply $filter on the array part. In mongoose you can apply the aggregation query in a more or less similar way https://mongoosejs.com/docs/api/aggregate.html
db.collection.aggregate([
{
$project: {
"ItemsPrices": {
$filter: {
input: "$ItemsPrices",
as: "item",
cond: {
$eq: [
"$$item._id",
mongoose.Types.ObjectId("620a971e11120abbde5f4c3b")
]
}
}
},
"__v": 1 //when projecting 1 means in the final result this field appears
}
}
])
more examples
demo

Option 1:
Use $filter in an aggregation query as explained by cmgchess
Option 2:
If you only want one object from array you can use $elemMatch like this:
db.collection.find({
"ItemsPrices._id": "620a971e11120abbde5f4c3b"
},
{
"ItemsPrices": {
"$elemMatch": {
"_id": "620a971e11120abbde5f4c3b"
}
}
})
Example here
But take care, using $elemMatch only the first element is returned. Check this other example where there are two objects with the desired _id but only returns one.
As said before, if you only one (or only exists one) maybe you can use find and $elemMatch to avoid a filter by the entire array. But if can be multiple values use $filter.

Mongoose fetch localization multilingual

I'm using nodejs with mongoose (mongodb) and I want to filter inside a subdocument array the language selected.
User schema:
var localUserSchema = new mongoose.Schema({
firstName: {
type: String
},
moreInformation: {
experience: {
type: Number
},
specializations: [{
...
sports:[{
type: Schema.Types.ObjectId,
ref: 'sport'
}]
}]
});
User data:
[{
"_id": {
"$oid": "5fc6a379b1d5ff2c42a9a536"
},
"moreInformation": {
"experience" : 2,
"specializations": [{
"sports": [{
"$oid": "5fc6aa91b1db6cd15702241c"
}, {
"$oid": "5fcb741e786f0703646befe2"
}]
}]
}
}]
Sport schema:
var sportSchema = new Schema({
name: {
en: {
type: String
},
it: {
type: String
}
},
icon: {
type: Schema.Types.ObjectId, ref: 'file'
}
});
Sport data:
[{
"_id": {
"$oid": "5fc6aa91b1db6cd15702241c"
},
"name": {
"en": "Football",
"it": "Calcio"
},
"icon": {
"$oid": "5fc9598a0955177dee8a3bc4"
}
},{
"_id": {
"$oid": "5fcb741e786f0703646befe2"
},
"name": {
"en": "Swimming",
"it": "Nuoto"
},
"icon": {
"$oid": "5fc9598a0955177dee8a3bc5"
}
}
I want all users joined with sports by sport id, but filtered by language key like below and replace the sports name languages with the name selected without the language key.
So, if I wanted to select and filter the english language 'en', i would like to get this result:
[
{
"_id": "5fc6a379b1d5ff2c42a9a536",
"moreInformation": {
"specializations": [{
...
"sports": [
{
"_id": "5fc6aa91b1db6cd15702241c",
"name": "Football",
"icon": "5fc9598a0955177dee8a3bc4"
},
{
"_id": "5fcb741e786f0703646befe2",
"name": "Swimming",
"icon": "5fc9598a0955177dee8a3bc5"
}]
}]
}
}
}
How I can do it?

You will need to use aggregation methods like $unwind, $lookup, $group last but not least $project.
They define a sequence of steps to help you retrieve your data as you expect
The get the response that you want take a look into the following code and the running example in here
Ps: I suggest you to look into the example in the mongo playground ( link above ) and separate the aggregation pipelines to understand better the proccess
db.users.aggregate([
{
// move specializations array to separated objects
"$unwind": "$moreInformation.specializations"
},
{
// move specialization.sports to separated objects
"$unwind": "$moreInformation.specializations.sports"
},
{
// search into sports collection based on the temporary "sports" attribute
$lookup: {
from: "sports",
localField: "moreInformation.specializations.sports",
foreignField: "_id",
as: "fullSport"
}
},
{
// as the lookup resolves an array of a single result we move it to be an object
"$unwind": "$fullSport"
},
{
// here we select only the attributes that we need and the selected language
"$project": {
"moreInformation.experience": 1,
"moreInformation.specializations.sports._id": "$fullSport._id",
"moreInformation.specializations.sports.icon": "$fullSport.icon",
"moreInformation.specializations.sports.name": "$fullSport.name.en"
}
},
{
// then we group it to make the separated objects an array again
"$group": {
"_id": "$_id",
// we group by the $_id and move it to temporary "sports" attribute
"sports": {
$push: "$moreInformation.specializations.sports"
},
"moreInformation": {
$first: "$moreInformation"
}
}
},
{
$project: {
"moreInformation.experience": 1,
// move back the temporary "sports" attribute to its previous path
"moreInformation.specializations.sports": "$sports"
}
}
])

Adding property to mulitple documents in mongoDB

I have this data structure:
{
"_id": "5ebd08794bcc8d2fd893f4a7",
"username": "johan#gmail.com",
"password": "123",
"decks": [{
"cards": [{
"_id": "5ebd08794bcc8d2fd893f4a9",
"planeetnaam": "Venus",
"kleur": "Grijs"
},
{
"_id": "5ebd08794bcc8d2fd893f4aa",
"planeetnaam": "Neptunus",
"kleur": "Paars"
}
],
"_id": "5ebd08794bcc8d2fd893f4a8",
"name": "Planeten"
},
{
"cards": [{
"_id": "5ebd08794bcc8d2fd893f4ac",
"diernaam": "Hond",
"poten": "4"
},
{
"_id": "5ebd08794bcc8d2fd893f4ad",
"diernaam": "Kangoeroe",
"poten": "2"
}
],
"_id": "5ebd08794bcc8d2fd893f4ab",
"name": "Dieren"
}
],
"__v": 0
}
Now i want to add a new property to all the cards in deck with deckname: "Planeten". How do i do this with a mongoose query?
The cards array of deck "Planeten" should look like this after the query
"cards": [{
"_id": "5ebd08794bcc8d2fd893f4a9",
"planeetnaam": "Venus",
"kleur": "Grijs",
"newProp": null
},
{
"_id": "5ebd08794bcc8d2fd893f4aa",
"planeetnaam": "Neptunus",
"kleur": "Paars",
"newProp": null
}
],
EDIT:
This works in Robo3T:
db.getCollection('users').findOneAndUpdate(
{ '_id': ObjectId("5eba9ee0abfaf237f81fb104") },
{ $set: { 'decks.$[deck].cards.$[].newProp': null } },
{ arrayFilters: [{ 'deck._id': ObjectId("5eba9ee0abfaf237f81fb108") } ] }
)
But the server query doesnt edit any data:
User.findOneAndUpdate(
{ '_id': req.session.userid },
{ $set: { 'decks.$[deck].cards.$[].newProp': null } },
{ arrayFilters: [{ 'deck._id': req.params.deckid } ] }, function(err, user){
res.send('test');
})
Thanks in advance

you can use array update operators
the query may look something like that
db.collection.updateOne(
{ _id: <ObjectId> }, // the filter part
{ $set: { 'decks.$[deck].cards.$[].newProp': null } },
{ arrayFilters: [{ 'deck.name': 'Planeten' }] }
)
$[deck] refers to each element in the decks array
$[] is used to update all the elements in the cards array
your function may look something like that
User.updateOne(
{ '_id': req.session.userid },
{ $set: { 'decks.$[deck].cards.$[].newProp': null } },
{ arrayFilters: [{ 'deck.name': 'Planeten' }] })
.then(function (user) {
if (!user) {
res.status(404).send('Er ging helaas iets fout')
} else {
res.status(201).send("Card is toegevoegd");
}
})
hope it helps

Mongoose find with multiple matches

I'm new to this technology and working with Node and Express server that uses Mongoose. I have following schema for a document collection.
var empSchema = new mongoose.Schema({
_id: String,
orgName: {type: String, required: true},
locName: {type: String, required: true},
empName: {type: String, required: true}
});
Here I get a list of location names like "NewYork", "London", "Paris" etc... in a request and needs to return the documents in the response as following....
{
result:[{locName:"NewYork",
empList:[
{orgName:"abc", empName:"emp1"},
{orgName:"xyz", empName:"emp2"}]
},
{locName:"London",
empList:[
{orgName:"pkq", empName:"emp13"},
{orgName:"mns", empName:"emp23"}]
}]
}
What would be the best way to use mongoose from Node. I think making multiple queries (each one with a location) to mongodb is a bad idea.
Is there a way to get the expected json response with single call to mongoose? Thanks.

Yes, use the aggregation framework to get the desired output. The aggregation pipeline will consist of a $group operator pipeline stage which groups the documents by the locName field and the $addToSet accumulator operator to add the orgName and empName fields to an array empList. The last pipeline stage $project operator then replaces the _id field from the previous aggregation stream with a new field locName.
To demonstrate this concept, suppose you have a sample collection which you insert with mongo shell:
db.employees.insert([
{
_id: "1",
orgName: "abc",
locName: "New York",
empName: "emp1"
},
{
_id: "2",
orgName: "xyz",
locName: "New York",
empName: "emp2"
},
{
_id: "3",
orgName: "pkq",
locName: "London",
empName: "emp13"
},
{
_id: "4",
orgName: "mns",
locName: "London",
empName: "emp23"
}
])
The following aggregation produces the desired result:
db.employees.aggregate([
{
"$group": {
"_id": "$locName",
"empList": {
"$addToSet": {
"orgName": "$orgName",
"empName": "$empName"
}
}
}
},
{
"$project": {
"_id": 0,
"locName": "$_id",
"empList": 1
}
}
])
Output:
/* 0 */
{
"result" : [
{
"empList" : [
{
"orgName" : "mns",
"empName" : "emp23"
},
{
"orgName" : "pkq",
"empName" : "emp13"
}
],
"locName" : "London"
},
{
"empList" : [
{
"orgName" : "xyz",
"empName" : "emp2"
},
{
"orgName" : "abc",
"empName" : "emp1"
}
],
"locName" : "New York"
}
],
"ok" : 1
}
In Mongoose, you can use the aggregation pipeline builder like this:
Employee.aggregate()
.group({
"_id": "$locName",
"empList": {
"$addToSet": {
"orgName": "$orgName",
"empName": "$empName"
}
}
})
.project({
"_id": 0,
"locName": "$_id",
"empList": 1
})
.exec(function (err, res) {
if (err) return handleError(err);
console.log(res);
});
// Or the simple aggregate method
var pipeline = [
{
"$group": {
"_id": "$locName",
"empList": {
"$addToSet": {
"orgName": "$orgName",
"empName": "$empName"
}
}
}
},
{
"$project": {
"_id": 0,
"locName": "$_id",
"empList": 1
}
}
]
Employee.aggregate(pipeline, function (err, res) {
if (err) return handleError(err);
console.log(res);
});

All queries, when you need to group by sum values called aggregate. You can read about it in the mongo docs and same methods have model in Mongoose. To produce your query, you can use code like this:
Employee
.aggregate()
.group({ _id: '$locName', empList: { $push: "$$ROOT" }})
.exec(function (err, res) {
});
If you need not to query all table, there is also have a match method.