I have an 'articles' collection, some sample data might look like this:
[
{body: 'Interesting news in Siberia and so on etc. etc. etc. and lolcats too',
author: 'John Doe',
tags: [{tid:24, name: "Siberia"},
{tid: 5231, name: "Lolcats"},]
},
{body: 'Something is going on in Siberia and France',
author: 'Jane Doe',
tags: [{tid:24, name: "Siberia"},
{tid: 6432, name: "France"},]
},
]
And my required ouput is a distinct list of tags:
[
{tid: 24, name: 'Siberia'},
{tid: 5231, name: 'Lolcats'},
{tid: 6432, name: 'France'},
]
I have been struggling with some mapReduce queries and distinct aggregation, but without result.
The simplest way to do this is:
db.articles.distinct("tags")
If you want to use aggregation framework (new in 2.2) it's a little longer:
db.articles.aggregate([{$unwind:"$tags"},
{$group:{_id:"$tags"}},
{$project:{tid:"$_id.tid",name:"$_id.name",_id:0}}
]).result
In mongo v2.2 you can do this with the aggregate function:
db.articles.aggregate([
{
// From each document, emit just the tags
$project: {
tags: 1
}
}, {
// Duplicate each document for each tags element it contains
$unwind: '$tags'
}, {
// Group the documents by the tag's tid and name
$group: {
_id: { tid: '$tags.tid', name: '$tags.name' }
}
}, {
// Reshape the document to exclude the _id and bring tid and name to the top level
$project: {
_id: 0,
tid: '$_id.tid',
name: '$_id.name'
}
}],
function (err, result) {
if (err) {
console.log('aggregation error: %s', err);
} else {
console.dir(result);
}
});
For your documents, this produces the following output:
[ { tid: 6432, name: 'France' },
{ tid: 5231, name: 'Lolcats' },
{ tid: 24, name: 'Siberia' } ]
db.articles.distinct("tags")
gives the following output:
[
{
"tid" : 24,
"name" : "Siberia"
},
{
"tid" : 5231,
"name" : "Lolcats"
},
{
"tid" : 6432,
"name" : "France"
}
]
Related
I also checked the following question and tried various other things but
couldn't get it working
Retrieve only the queried element in an object array in MongoDB collection
I have the following document sample
{
_id: ObjectId("634b08f7eb5cb6af473e3ab2"),
name: 'India',
iso_code: 'IN',
states: [
{
name: 'Karnataka',
cities: [
{
name: 'Hubli Tabibland',
pincode: 580020,
location: { type: 'point', coordinates: [Array] }
},
{
name: 'Hubli Vinobanagar',
pincode: 580020,
location: { type: 'point', coordinates: [Array] }
},
{
name: 'Hubli Bengeri',
pincode: 580023,
location: { type: 'point', coordinates: [Array] }
},
{
name: 'Kusugal',
pincode: 580023,
location: { type: 'point', coordinates: [Array] }
}
]
}
]
}
I need only the following
{
_id: ObjectId("634b08f7eb5cb6af473e3ab2"),
name: 'India',
iso_code: 'IN',
states: [
{
name: 'Karnataka',
cities: [
{
name: 'Kusugal',
pincode: 580023,
location: { type: 'point', coordinates: [Array] }
}
]
}
]
}
Following is the query that I have tried so far but it returns all the cities
db.countries.find(
{
'states.cities': {
$elemMatch: {
'name' : 'Kusugal'
}
}
},
{
'_id': 1,
'name': 1,
'states.name': 1,
'states.cities.$' : 1
}
);
I was able to achieve it with the help of aggregation.
db.countries.aggregate([
{ $match: { "states.cities.name": /Kusugal/ } },
{ $unwind: "$states" },
{ $unwind: "$states.cities" },
{ $match: { "states.cities.name": /Kusugal/ } }
]);
1st line $match will query the records with cities with only Kusugal
2nd & 3rd line $unwind will create a separate specific collection of documents from the filtered records
3rd line $match will filter these records again based on the condition
In simple aggregation processes commands and sends to next command and returns as an single result.
If a have a following structure :
{
_id: 1,
name: 'a',
info: []
},
{
_id: 2,
name: 'b',
info: [
{
infoID: 100,
infoData: 'my info'
}
]
},
{
_id: 3,
name: 'c',
info: [
{
infoID: 200,
infoData: 'some info 200'
},
{
infoID: 300,
infoData: 'some info 300'
}
]
}
I need to query in such a way to obtain the documents where infoID is 100 showing the infoData, or nothing if info is empty, or contains subdocuments with infoID different from 100.
That is, I would want the following output:
{
_id: 1,
name: 'a',
infoData100: null
},
{
_id: 2,
name: 'b',
infoData100: 'my info'
},
{
_id: 3,
name: 'c',
infoData100: null
}
If I $unwind by info and $match by infoID: 100, I lose records 1 and 3.
Thanks for your responses.
Try below query :
Query :
db.collection.aggregate([
/** Adding a new field or you can use $project instead of addFields */
{
$addFields: {
infoData100: {
$cond: [
{
$in: [100, "$info.infoID"] // Check if any of objects 'info.infoID' has value 100
},
{
// If any of those has get that object & get infoData & assign it to 'infoData100' field
$let: {
vars: {
data: {
$arrayElemAt: [
{
$filter: {
input: "$info",
cond: { $eq: ["$$this.infoID", 100] }
}
},
0
]
}
},
in: "$$data.infoData"
}
},
null // If none has return NULL
]
}
}
}
]);
Test : MongoDB-Playground
I have a document structure that is deeply nested, like this:
{id: 1,
forecasts: [ {
forecast_id: 123,
name: "Forecast 1",
levels: [
{ level: "proven",
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
},
{ level: "likely",
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
}
]
},
]
}
I'm trying to update the collection to insert a new config, that looks like this:
newdata = {
config: "Custom 1",
variables: [{ x: 111, y:2222, z:3333}]
}
I'm trying something like this in mongo (in Python):
db.myCollection.update({"id": 1,
"forecasts.forecast-id": 123,
"forecasts.levels.level": "proven",
"forecasts.levels.configs.config": "Custom 1"
},
{"$set": {"forecasts.$.levels.$.configs.$": newData}}
)
I'm getting "Cannot apply the positional operator without a corresponding query field containing an array" error though. What is the proper way to do this in mongo? This is mongo v2.4.1.
Unfortunately, you can't use the $ operator more than once per key, so you have to use numeric values for the rest. As in:
db.myCollection.update({
"id": 1,
"forecasts.forecast-id": 123,
"forecasts.levels.level": "proven",
"forecasts.levels.configs.config": "Custom 1"
},
{"$set": {"forecasts.$.levels.0.configs.0": newData}}
)
MongoDB's support for updating nested arrays is poor. So you're best off avoiding their use if you need to update the data frequently, and consider using multiple collections instead.
One possibility: make forecasts its own collection, and assuming you have a fixed set of level values, make level an object instead of an array:
{
_id: 123,
parentId: 1,
name: "Forecast 1",
levels: {
proven: {
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
},
likely: {
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
}
}
}
Then you can update it using:
db.myCollection.update({
_id: 123,
'levels.proven.configs.config': 'Custom 1'
},
{ $set: { 'levels.proven.configs.$': newData }}
)
Managed to solve it with using mongoose:
All you need to know is the '_id's of all of the sub-document in the chain (mongoose automatically create '_id' for each sub-document).
for example -
SchemaName.findById(_id, function (e, data) {
if (e) console.log(e);
data.sub1.id(_id1).sub2.id(_id2).field = req.body.something;
// or if you want to change more then one field -
//=> var t = data.sub1.id(_id1).sub2.id(_id2);
//=> t.field = req.body.something;
data.save();
});
More about the sub-document _id method in mongoose documentation.
explanation:_id is for the SchemaName, _id1 for sub1 and _id2 for sub2 - you can keep chaining like that.
*You don't have to use findById method, but it's seem to me the most convenient as you need to know the rest of the '_id's anyway.
MongoDB has introduced ArrayFilters to tackle this issue in Version 3.5.2 and later.
New in version 3.6.
Starting in MongoDB 3.6, when updating an array field, you can specify
arrayFilters that determine which array elements to update.
[https://docs.mongodb.com/manual/reference/method/db.collection.update/#specify-arrayfilters-for-an-array-update-operations][1]
Let's say the Schema design as follows :
var ProfileSchema = new Schema({
name: String,
albums: [{
tour_name: String,
images: [{
title: String,
image: String
}]
}]
});
And Document created looks like this :
{
"_id": "1",
"albums": [{
"images": [
{
"title": "t1",
"url": "url1"
},
{
"title": "t2",
"url": "url2"
}
],
"tour_name": "london-trip"
},
{
"images": [.........]:
}]
}
Say I want to update the "url" of an image.
Given - "document id", "tour_name" and "title"
For this the update query :
Profiles.update({_id : req.body.id},
{
$set: {
'albums.$[i].images.$[j].title': req.body.new_name
}
},
{
arrayFilters: [
{
"i.tour_name": req.body.tour_name, "j.image": req.body.new_name // tour_name - current tour name, new_name - new tour name
}]
})
.then(function (resp) {
console.log(resp)
res.json({status: 'success', resp});
}).catch(function (err) {
console.log(err);
res.status(500).json('Failed');
})
This is a very OLD bug in MongoDB
https://jira.mongodb.org/browse/SERVER-831
I was facing same kind of problem today, and after lot of exploring on google/stackoverflow/github, I figured arrayFilters are the best solution to this problem. Which would work with mongo 3.6 and above.
This link finally saved my day: https://thecodebarbarian.com/a-nodejs-perspective-on-mongodb-36-array-filters.html
const OrganizationInformationSchema = mongoose.Schema({
user: {
_id: String,
name: String
},
organizations: [{
name: {
type: String,
unique: true,
sparse: true
},
rosters: [{
name: {
type: String
},
designation: {
type: String
}
}]
}]
}, {
timestamps: true
});
And using mongoose in express, updating the name of roster of given id.
const mongoose = require('mongoose');
const ControllerModel = require('../models/organizations.model.js');
module.exports = {
// Find one record from database and update.
findOneRosterAndUpdate: (req, res, next) => {
ControllerModel.updateOne({}, {
$set: {
"organizations.$[].rosters.$[i].name": req.body.name
}
}, {
arrayFilters: [
{ "i._id": mongoose.Types.ObjectId(req.params.id) }
]
}).then(response => {
res.send(response);
}).catch(err => {
res.status(500).send({
message: "Failed! record cannot be updated.",
err
});
});
}
}
It's fixed.
https://jira.mongodb.org/browse/SERVER-831
But this feature is available starting with the MongoDB 3.5.12 development version.
Note: This question asked on Aug 11 2013 and it's resolved on Aug 11 2017
Given how MongoDB doesn't appear to provide a good mechanism for this, I find it prudent to use mongoose to simply extract the element from the mongo collection using .findOne(...), run a for-loop search on its relevant subelements (seeking by say ObjectID), modify that JSON, then do Schema.markModified('your.subdocument'); Schema.save(); It's probably not efficient, but it is very simple and works fine.
I searched about this for about 5 hours and finally found the best and easiest solution:
HOW TO UPDATE NESTED SUB-DOCUMENTS IN MONGO DB
{id: 1,
forecasts: [ {
forecast_id: 123,
name: "Forecast 1",
levels: [
{
levelid:1221
levelname: "proven",
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
},
{
levelid:1221
levelname: "likely",
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
}
]
},
]}
Query:
db.weather.updateOne({
"_id": ObjectId("1"), //this is level O select
"forecasts": {
"$elemMatch": {
"forecast_id": ObjectId("123"), //this is level one select
"levels.levelid": ObjectId("1221") // this is level to select
}
}
},
{
"$set": {
"forecasts.$[outer].levels.$[inner].levelname": "New proven",
}
},
{
"arrayFilters": [
{ "outer.forecast_id": ObjectId("123") },
{ "inner.levelid": ObjectId("1221") }
]
}).then((result) => {
resolve(result);
}, (err) => {
reject(err);
});
Sharing my lessons learned. I faced the same requirement recently where i need to update a nested array item.
My structure is as follows
{
"main": {
"id": "ID_001",
"name": "Fred flinstone Inc"
},
"types": [
{
"typeId": "TYPE1",
"locations": [
{
"name": "Sydney",
"units": [
{
"unitId": "PHG_BTG1"
}
]
},
{
"name": "Brisbane",
"units": [
{
"unitId": "PHG_KTN1"
},
{
"unitId": "PHG_KTN2"
}
]
}
]
}
]
}
My requirement is to add some fields in a specific units[].
My solution is first to find the index of the nested array item (say foundUnitIdx)
The two techniques I used are
use the $set keyword
specify the dynamic field in $set using the [] syntax
query = {
"locations.units.unitId": "PHG_KTN2"
};
var updateItem = {
$set: {
["locations.$.units."+ foundUnitIdx]: unitItem
}
};
var result = collection.update(
query,
updateItem,
{
upsert: true
}
);
Hope this helps others. :)
EASY SOLUTION FOR Mongodb 3.2+
https://docs.mongodb.com/manual/reference/method/db.collection.replaceOne/
I had a similar situation and solved it like this. I was using mongoose, but it should still work in vanilla MongoDB. Hope it's useful to someone.
const MyModel = require('./model.js')
const query = {id: 1}
// First get the doc
MyModel.findOne(query, (error, doc) => {
// Do some mutations
doc.foo.bar.etc = 'some new value'
// Pass in the mutated doc and replace
MyModel.replaceOne(query, doc, (error, newDoc) => {
console.log('It worked!')
})
}
Depending on your use case, you might be able to skip the initial findOne()
Okkk.we can update our nested subdocument in mongodb.this is our schema.
var Post = new mongoose.Schema({
name:String,
post:[{
like:String,
comment:[{
date:String,
username:String,
detail:{
time:String,
day:String
}
}]
}]
})
solution for this schema
Test.update({"post._id":"58206a6aa7b5b99e32b7eb58"},
{$set:{"post.$.comment.0.detail.time":"aajtk"}},
function(err,data){
//data is updated
})
I have a document structure that is deeply nested, like this:
{id: 1,
forecasts: [ {
forecast_id: 123,
name: "Forecast 1",
levels: [
{ level: "proven",
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
},
{ level: "likely",
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
}
]
},
]
}
I'm trying to update the collection to insert a new config, that looks like this:
newdata = {
config: "Custom 1",
variables: [{ x: 111, y:2222, z:3333}]
}
I'm trying something like this in mongo (in Python):
db.myCollection.update({"id": 1,
"forecasts.forecast-id": 123,
"forecasts.levels.level": "proven",
"forecasts.levels.configs.config": "Custom 1"
},
{"$set": {"forecasts.$.levels.$.configs.$": newData}}
)
I'm getting "Cannot apply the positional operator without a corresponding query field containing an array" error though. What is the proper way to do this in mongo? This is mongo v2.4.1.
Unfortunately, you can't use the $ operator more than once per key, so you have to use numeric values for the rest. As in:
db.myCollection.update({
"id": 1,
"forecasts.forecast-id": 123,
"forecasts.levels.level": "proven",
"forecasts.levels.configs.config": "Custom 1"
},
{"$set": {"forecasts.$.levels.0.configs.0": newData}}
)
MongoDB's support for updating nested arrays is poor. So you're best off avoiding their use if you need to update the data frequently, and consider using multiple collections instead.
One possibility: make forecasts its own collection, and assuming you have a fixed set of level values, make level an object instead of an array:
{
_id: 123,
parentId: 1,
name: "Forecast 1",
levels: {
proven: {
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
},
likely: {
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
}
}
}
Then you can update it using:
db.myCollection.update({
_id: 123,
'levels.proven.configs.config': 'Custom 1'
},
{ $set: { 'levels.proven.configs.$': newData }}
)
Managed to solve it with using mongoose:
All you need to know is the '_id's of all of the sub-document in the chain (mongoose automatically create '_id' for each sub-document).
for example -
SchemaName.findById(_id, function (e, data) {
if (e) console.log(e);
data.sub1.id(_id1).sub2.id(_id2).field = req.body.something;
// or if you want to change more then one field -
//=> var t = data.sub1.id(_id1).sub2.id(_id2);
//=> t.field = req.body.something;
data.save();
});
More about the sub-document _id method in mongoose documentation.
explanation:_id is for the SchemaName, _id1 for sub1 and _id2 for sub2 - you can keep chaining like that.
*You don't have to use findById method, but it's seem to me the most convenient as you need to know the rest of the '_id's anyway.
MongoDB has introduced ArrayFilters to tackle this issue in Version 3.5.2 and later.
New in version 3.6.
Starting in MongoDB 3.6, when updating an array field, you can specify
arrayFilters that determine which array elements to update.
[https://docs.mongodb.com/manual/reference/method/db.collection.update/#specify-arrayfilters-for-an-array-update-operations][1]
Let's say the Schema design as follows :
var ProfileSchema = new Schema({
name: String,
albums: [{
tour_name: String,
images: [{
title: String,
image: String
}]
}]
});
And Document created looks like this :
{
"_id": "1",
"albums": [{
"images": [
{
"title": "t1",
"url": "url1"
},
{
"title": "t2",
"url": "url2"
}
],
"tour_name": "london-trip"
},
{
"images": [.........]:
}]
}
Say I want to update the "url" of an image.
Given - "document id", "tour_name" and "title"
For this the update query :
Profiles.update({_id : req.body.id},
{
$set: {
'albums.$[i].images.$[j].title': req.body.new_name
}
},
{
arrayFilters: [
{
"i.tour_name": req.body.tour_name, "j.image": req.body.new_name // tour_name - current tour name, new_name - new tour name
}]
})
.then(function (resp) {
console.log(resp)
res.json({status: 'success', resp});
}).catch(function (err) {
console.log(err);
res.status(500).json('Failed');
})
This is a very OLD bug in MongoDB
https://jira.mongodb.org/browse/SERVER-831
I was facing same kind of problem today, and after lot of exploring on google/stackoverflow/github, I figured arrayFilters are the best solution to this problem. Which would work with mongo 3.6 and above.
This link finally saved my day: https://thecodebarbarian.com/a-nodejs-perspective-on-mongodb-36-array-filters.html
const OrganizationInformationSchema = mongoose.Schema({
user: {
_id: String,
name: String
},
organizations: [{
name: {
type: String,
unique: true,
sparse: true
},
rosters: [{
name: {
type: String
},
designation: {
type: String
}
}]
}]
}, {
timestamps: true
});
And using mongoose in express, updating the name of roster of given id.
const mongoose = require('mongoose');
const ControllerModel = require('../models/organizations.model.js');
module.exports = {
// Find one record from database and update.
findOneRosterAndUpdate: (req, res, next) => {
ControllerModel.updateOne({}, {
$set: {
"organizations.$[].rosters.$[i].name": req.body.name
}
}, {
arrayFilters: [
{ "i._id": mongoose.Types.ObjectId(req.params.id) }
]
}).then(response => {
res.send(response);
}).catch(err => {
res.status(500).send({
message: "Failed! record cannot be updated.",
err
});
});
}
}
It's fixed.
https://jira.mongodb.org/browse/SERVER-831
But this feature is available starting with the MongoDB 3.5.12 development version.
Note: This question asked on Aug 11 2013 and it's resolved on Aug 11 2017
Given how MongoDB doesn't appear to provide a good mechanism for this, I find it prudent to use mongoose to simply extract the element from the mongo collection using .findOne(...), run a for-loop search on its relevant subelements (seeking by say ObjectID), modify that JSON, then do Schema.markModified('your.subdocument'); Schema.save(); It's probably not efficient, but it is very simple and works fine.
I searched about this for about 5 hours and finally found the best and easiest solution:
HOW TO UPDATE NESTED SUB-DOCUMENTS IN MONGO DB
{id: 1,
forecasts: [ {
forecast_id: 123,
name: "Forecast 1",
levels: [
{
levelid:1221
levelname: "proven",
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
},
{
levelid:1221
levelname: "likely",
configs: [
{
config: "Custom 1",
variables: [{ x: 1, y:2, z:3}]
},
{
config: "Custom 2",
variables: [{ x: 10, y:20, z:30}]
},
]
}
]
},
]}
Query:
db.weather.updateOne({
"_id": ObjectId("1"), //this is level O select
"forecasts": {
"$elemMatch": {
"forecast_id": ObjectId("123"), //this is level one select
"levels.levelid": ObjectId("1221") // this is level to select
}
}
},
{
"$set": {
"forecasts.$[outer].levels.$[inner].levelname": "New proven",
}
},
{
"arrayFilters": [
{ "outer.forecast_id": ObjectId("123") },
{ "inner.levelid": ObjectId("1221") }
]
}).then((result) => {
resolve(result);
}, (err) => {
reject(err);
});
Sharing my lessons learned. I faced the same requirement recently where i need to update a nested array item.
My structure is as follows
{
"main": {
"id": "ID_001",
"name": "Fred flinstone Inc"
},
"types": [
{
"typeId": "TYPE1",
"locations": [
{
"name": "Sydney",
"units": [
{
"unitId": "PHG_BTG1"
}
]
},
{
"name": "Brisbane",
"units": [
{
"unitId": "PHG_KTN1"
},
{
"unitId": "PHG_KTN2"
}
]
}
]
}
]
}
My requirement is to add some fields in a specific units[].
My solution is first to find the index of the nested array item (say foundUnitIdx)
The two techniques I used are
use the $set keyword
specify the dynamic field in $set using the [] syntax
query = {
"locations.units.unitId": "PHG_KTN2"
};
var updateItem = {
$set: {
["locations.$.units."+ foundUnitIdx]: unitItem
}
};
var result = collection.update(
query,
updateItem,
{
upsert: true
}
);
Hope this helps others. :)
EASY SOLUTION FOR Mongodb 3.2+
https://docs.mongodb.com/manual/reference/method/db.collection.replaceOne/
I had a similar situation and solved it like this. I was using mongoose, but it should still work in vanilla MongoDB. Hope it's useful to someone.
const MyModel = require('./model.js')
const query = {id: 1}
// First get the doc
MyModel.findOne(query, (error, doc) => {
// Do some mutations
doc.foo.bar.etc = 'some new value'
// Pass in the mutated doc and replace
MyModel.replaceOne(query, doc, (error, newDoc) => {
console.log('It worked!')
})
}
Depending on your use case, you might be able to skip the initial findOne()
Okkk.we can update our nested subdocument in mongodb.this is our schema.
var Post = new mongoose.Schema({
name:String,
post:[{
like:String,
comment:[{
date:String,
username:String,
detail:{
time:String,
day:String
}
}]
}]
})
solution for this schema
Test.update({"post._id":"58206a6aa7b5b99e32b7eb58"},
{$set:{"post.$.comment.0.detail.time":"aajtk"}},
function(err,data){
//data is updated
})
I have following documents in my collection
{
_id: ObjectId("5166fefbc482c31052000002"),
contact: [
{
home: 7735734105
},
{
office: 9583866301
}
],
user_name: "moti",
reportsTo: "bikram",
technology: [
{
name: ".net",
rating: 5
},
{
name: "JavaScript",
rating: 2
}
],
project: [
"Agile School",
"Draftmate"
],
type: "developer",
email: "motiranjan.pradhan#ajatus.co.in"
}
and
{
_id: ObjectId("5166fe90c482c31052000001"),
contact: [
{
home: 7735734103
},
{
office: 9583866901
}
],
user_name: "ganesh",
reportsTo: "bikram",
technology: [
{
name: "JavaScript",
rating: 3
},
{
name: ".net",
rating: 4
}
],
project: [
"SLBC",
"Draftmate"
],
type: "developer",
email: "ganesh.patra#ajatus.co.in"
}
Now I need to find the rating of the people who know only JavaScript.Currently if I run
db.users.find(
{
technology: {
$elemMatch: {
name: 'JavaScript'
}
}
},{user_name:1,'technology.name':1,_id:0}
).pretty()
I am getting names of all technologies(.net & JavaScript) and their corresponding ratings. I need only user names,and their respective ratings in JavaScript only. Do I need to use any aggregation techniques?
The positional operator '$' can be used to limit query results to the first matching element. To use in your query above you would change it to:
db.users.find( { technology: { $elemMatch: { name: 'JavaScript' } } },{user_name:1,'technology.$.name':1,_id:0} )