One of my mongodb collection is
{_id: "1", username: "one"}
{_id: "2", username: "two"}
{_id: "3", username: "three"}
......
{_id: "50", username: "fifty"}
I want to query the collection to get the values of all the "username" keys in whole collection as:
["one","two","three",.... "fifty"]
I've tried this so far and it yields the results as:
db.users.find({}, { username: 1, _id: 0 })
// output: [ { username: "one" }, { username: "two" }, ..... ]
Make use of the $group stage via Aggregation and group all the documents in the collection and push the required value to an array.
db.collection.aggregate([
{
"$group": {
"_id": null,
"usernames": {
"$push": "$username"
}
},
},
])
If you want distinct values of usernames, replace $push with $addToSet instead.
I get a document from a mongodb which contains an array with comments for that document. In the comment is the _id of the user which wrote the comment.
I now need to get the username based on the _id of the user, but I'm running into several problems.
I have the following code which, obviously, doesn't work, but I hope it can give you an idea of what I'm trying to accomplish.
//MORE CODE... (No need to show this here, just a promise, some try catch and so on)
let article = await Article.findOne({_id:articleid})
for(var i = 0; i<=article.comment.length-1; i++){
User.findOne({_id:article.comment[i].user}).then((user)=>{
article.comment[i].username = user.username
})
}
return resolve(article)
I looked up several documentations but wasn't able to find a working solution. I tried using Promise.all, played around with a lot of async, await, tried to add a counter into the for-loop and resolve the promise after the loop finished but nothing worked so far.
This is what the article looks like in my db
{
"_id" : ObjectId("5c18c1cbc47e5e29d42e4b0e"),
"completed" : false,
"completedAt" : null,
"comment" : [
{
"_id" : ObjectId("5c18c95e328c8319ac07d817"),
"comment" : "This is a comment",
"rating" : [ ],
"user" : ObjectId("5c18b76e73236d2168eda2b4")
},
{
"_id" : ObjectId("5c18fb578de5741f20a4e2bd"),
"comment" : "Another comment",
"rating" : [ ],
"user" : ObjectId("5c18b76e73236d2168eda2b4")
}
]
}
I'm rather new to nodejs and mongodb aswell so I hope you can help a newbie like me.
Thank you for your Help
There are serveral approaches you can use here based on your convenience
Using async await
let article = await Article.findOne({ _id: articleid }).lean().exec()
await Promise.all(
article.comment.map(async(obj) => {
const user = await User.findOne({ _id: obj.user })
obj.username = user.username
})
)
console.log(article)
Using $lookup aggregation 3.6
Since mongodb has its own powerfull $lookup aggregation operator to join multiple collection and probably the better approach without any iteration
Article.aggregate([
{ "$match": { "_id": mongoose.Types.ObjectId(articleid) }},
{ "$unwind": "$comment" },
{ "$lookup": {
"from": "users",
"let": { "userId": "$comment.user" },
"pipeline": [
{ "$match": { "$expr": { "$eq": ["$$userId", "$_id"] }}}
],
"as": "comment.user"
}},
{ "$unwind": "$comment.user" },
{ "$group": {
"_id": "$_id",
"comment": { "$push": "$comment" },
"completed": { "$first": "$completed" },
"completedAt": { "$first": "$completedAt" }
}}
])
Using $lookup aggregation 3.4
Article.aggregate([
{ "$match": { "_id": mongoose.Types.ObjectId(articleid) }},
{ "$unwind": "$comment" },
{ "$lookup": {
"from": "users",
"localField": "comment.user",
"foreignField": "_id",
"as": "comment.user"
}}
{ "$unwind": "$comment.user" },
{ "$group": {
"_id": "$_id",
"comment": { "$push": "$comment" },
"completed": { "$first": "$completed" },
"completedAt": { "$first": "$completedAt" }
}}
])
You can try like the following way
const d = {
"_id" : ObjectId("5c18c1cbc47e5e29d42e4b0e"),
"completed" : false,
"completedAt" : null,
"comment" : [
{
"_id" : ObjectId("5c18c95e328c8319ac07d817"),
"comment" : "This is a comment",
"rating" : [ ],
"user" : ObjectId("5c18b76e73236d2168eda2b4")
},
{
"_id" : ObjectId("5c18fb578de5741f20a4e2bd"),
"comment" : "Another comment",
"rating" : [ ],
"user" : ObjectId("5c18b76e73236d2168eda2b4")
}
]
}
d.comment.forEach( async (obj, index) => {
await new Promise((res) => {
obj.counter = index;
res();
})
});
console.log(d);
For reference please take a look on following link
Asycn/Await using forEach
i am struggling with a task, which it is I used two schemas
User Schema
{
"first_name": String,
"last_name":String,
"address": String
}
Employee schema
{
user:{
type: ObjectId,
ref: 'User'
},
gross_pay: String,
net_pay: String
tax: String,
}
Well, how can I search first_name using $regex in Employee Schema in this user referenced field? I tried in so many ways, can't get it. how can i resolve it? Thanks in advance
First Approach:
Using $lookup aggregation
Employee.aggregate([
{ "$lookup": {
"from": "users",
"let": { "user": "$user" },
"pipeline": [
{ "$match": { "$expr": { "$eq": ["$_id", "$$user"] }}},
{ "$project": { "firstName": 1 }}
],
"as": "user"
}},
{ "$unwind": "$user" },
{ "$match": { "user.firstName": { "$regex": your_string, "$options": "i" }}}
])
But it is not the better approach as the $lookup stage is being applied to all the Employee documents and then $match to the users firstName makes the query bit slow.
Second Approach:
First find the users having firstName equal to the match string using $regex and then find the _id in the Employee collection.
const userIds = await (Users.find({ "firstName": { "$regex": your_string, "$options": "i" } })).map(user => user._id)
const employees = await Employee.find({ "user": { "$in": userIds }})
Third Approach:
Keep the single key firstName of the user schema in the employee schema
Employee schema
user: { type: ObjectId, ref: 'User' },
gross_pay: String,
net_pay: String
tax: String
firstName: String
and then use query directly
const userIds = await Employee.find({
"firstName": { "$regex": your_string, "$options": "i" }
})
I've just tried MongoDB & NodeJS and having issue in finding specific array collections using Nodejs.
Here's the the collections I have :
{
"_id": ObjectId("552aa4da6e25e57ebde7ac6f"),
"username": "blablabla",
"email": "xxx#gmail.com",
"password": "Dummy Trip",
"itinerary": [
{
"_id": ObjectId("552c109adb616795044a919e"),
"title": "test-0",
"desc": "test-0-desc"
},
{
"_id": ObjectId("552c10b0db616795044a91a0"),
"title": "test-1",
"desc": "test-1-desc"
},
{
"_id": ObjectId("552c1128db616795044a91a1"),
"title": "test-2",
"desc": "test-2-desc"
}
]
}
So I need to find the array of itinerary that has objecId of "552c109adb616795044a919e"
In MongoDB terminal I use findOne command & positional $ operator and it works as expected, showing only the array I search for.
Command :
db.user.findOne({ "itinerary._id" : ObjectId("552c109adb616795044a919e") }, {"itinerary.$" : 1})
Result :
{
"_id" : ObjectId("552aa4da6e25e57ebde7ac6f"),
"itinerary" : [
{
"_id" : ObjectId("552c109adb616795044a919e"),
"title" : "test-0",
"desc" : "test-0-desc"
}
]}
But why when I tried to implement it in NodeJS, it shows all records instead of the specific array I search.
Here's my NodeJS :
var userCollection = db.get('user');
userCollection.findOne({ "itinerary._id" : new ObjectID("552c109adb616795044a919e") }, {"itinerary.$" : 1},function(e,userDocs){
console.log(userDocs);
});
NodeJS Result (Showing all results) :
{
_id: 552aa4da6e25e57ebde7ac6f,
username: 'blablabla',
email: 'xxx#gmail.com',
password: 'Dummy Trip',
itinerary: [
{
_id: 552c109adb616795044a919e,
title: 'test-0',
desc: 'test-0-desc'
},
{
_id: 552c10b0db616795044a91a0,
title: 'test-1',
desc: 'test-1-desc'
},
{
_id: 552c1128db616795044a91a1,
title: 'test-2',
desc: 'test-2-desc'
}
]
}
Did I miss something here ?
Note :
I'm using Node MongoDB native driver
Thanks in advance :)
I am assuming your itinerary is an array. then you will have to use $elemMatch in mongodb.More details on elemMatch.
You can try something like.
var userCollection = db.get('user');
userCollection.findOne({ "itinerary": { $elemMatch: {_id: new ObjectID("552c109adb616795044a919e")}}}, {"itinerary.$" : 1},function(e,userDocs){
console.log(userDocs);
});
Also i think for matching object id you can use mongoose.Types.ObjectId("552c109adb616795044a919e")
This is my appointment collection:
{ _id: ObjectId("518ee0bc9be1909012000002"), date: ISODate("2013-05-13T22:00:00Z"), patient:ObjectId("518ee0bc9be1909012000002") }
{ _id: ObjectId("518ee0bc9be1909012000002"), date: ISODate("2013-05-13T22:00:00Z"), patient:ObjectId("518ee0bc9be1909012000002") }
{ _id: ObjectId("518ee0bc9be1909012000002"), date: ISODate("2013-05-13T22:00:00Z"), patient:ObjectId("518ee0bc9be1909012000002") }
I used aggregate to get the following result
{date: ISODate("2013-05-13T22:00:00Z"),
patients:[ObjectId("518ee0bc9be1909012000002"),ObjectId("518ee0bc9be1909012000002"),ObjectId("518ee0bc9be1909012000002")] }
like this:
Appointments.aggregate([
{$group: {_id: '$date', patients: {$push: '$patient'}}},
{$project: {date: '$_id', patients: 1, _id: 0}}
], ...)
How can I populate the patient document
I trued this but it doesn't work ... Appointments.find({}).populate("patient").aggregate....
In other words, can i use populate and aggregate at the same statement
any help please
With the latest version of mongoose (mongoose >= 3.6), you can but it requires a second query, and using populate differently. After your aggregation, do this:
Patients.populate(result, {path: "patient"}, callback);
See more at the Mongoose API and the Mongoose docs.
Edit: Looks like there's a new way to do it in the latest Mongoose API (see the above answer here: https://stackoverflow.com/a/23142503/293492)
Old answer below
You can use $lookup which is similar to populate.
In an unrelated example, I use $match to query for records and $lookup to populate a foreign model as a sub-property of these records:
Invite.aggregate(
{ $match: {interview: req.params.interview}},
{ $lookup: {from: 'users', localField: 'email', foreignField: 'email', as: 'user'} }
).exec( function (err, invites) {
if (err) {
next(err);
}
res.json(invites);
}
);
You have to do it in two, not in one statement.
In async await scenario, make sure await until populate.
const appointments = await Appointments.aggregate([...]);
await Patients.populate(appointments, {path: "patient"});
return appointments;
or (if you want to limit)
await Patients.populate(appointments, {path: "patient", select: {_id: 1, fullname: 1}});
You can do it in one query like this:
Appointments.aggregate([{
$group: {
_id: '$date',
patients: {
$push: '$patient'
}
}
},
{
$project: {
date: '$_id',
patients: 1,
_id: 0
}
},
{
$lookup: {
from: "patients",
localField: "patient",
foreignField: "_id",
as: "patient_doc"
}
}
])
populate basically uses $lookup under the hood.
in this case no need for a second query.
for more details check MongoDB aggregation lookup
Perform a Join with $lookup
A collection orders contains the following documents:
{ "_id" : 1, "item" : "abc", "price" : 12, "quantity" : 2 }
{ "_id" : 2, "item" : "jkl", "price" : 20, "quantity" : 1 }
{ "_id" : 3 }
Another collection inventory contains the following documents:
{ "_id" : 1, "sku" : "abc", description: "product 1", "instock" : 120 }
{ "_id" : 2, "sku" : "def", description: "product 2", "instock" : 80 }
{ "_id" : 3, "sku" : "ijk", description: "product 3", "instock" : 60 }
{ "_id" : 4, "sku" : "jkl", description: "product 4", "instock" : 70 }
{ "_id" : 5, "sku": null, description: "Incomplete" }
{ "_id" : 6 }
The following aggregation operation on the orders collection joins the documents from orders with the documents from the inventory collection using the fields item from the orders collection and the sku field from the inventory collection:
db.orders.aggregate([
{
$lookup:
{
from: "inventory",
localField: "item",
foreignField: "sku",
as: "inventory_docs"
}
}
])
The operation returns the following documents:
{
"_id" : 1,
"item" : "abc",
"price" : 12,
"quantity" : 2,
"inventory_docs" : [
{ "_id" : 1, "sku" : "abc", description: "product 1", "instock" : 120 }
]
}
{
"_id" : 2,
"item" : "jkl",
"price" : 20,
"quantity" : 1,
"inventory_docs" : [
{ "_id" : 4, "sku" : "jkl", "description" : "product 4", "instock" : 70 }
]
}
{
"_id" : 3,
"inventory_docs" : [
{ "_id" : 5, "sku" : null, "description" : "Incomplete" },
{ "_id" : 6 }
]
}
Reference $lookup
Short answer:
You can't.
Long answer:
In the Aggregation Framework, the returned fields are built by you, and you're able to "rename" document properties.
What this means is that Mongoose can't identify that your referenced documents will be available in the final result.
The best thing you can do in such a situation is populate the field you want after the query has returned. Yes, that would result in two DB calls, but it's what MongoDB allows us to do.
Somewhat like this:
Appointments.aggregate([ ... ], function( e, result ) {
if ( e ) return;
// You would probably have to do some loop here, as probably 'result' is array
Patients.findOneById( result.patient, function( e, patient ) {
if ( e ) return;
result.patient = patient;
});
});
domain.Farm.aggregate({
$match: {
"_id": mongoose.Types.ObjectId(farmId)
}
}, {
$unwind: "$SelfAssessment"
}, {
$match: {
"SelfAssessment.questionCategoryID": QuesCategoryId,
"SelfAssessment.questionID": quesId
}
},function(err, docs) {
var options = {
path: 'SelfAssessment.actions',
model: 'FarmAction'
};
domain.Farm.populate(docs, options, function (err, projects) {
callback(err,projects);
});
});
results i got action model populate
{ "error": false, "object": [
{
"_id": "57750cf6197f0b5137d259a0",
"createdAt": "2016-06-30T12:13:42.299Z",
"updatedAt": "2016-06-30T12:13:42.299Z",
"farmName": "abb",
"userId": "57750ce2197f0b5137d2599e",
"SelfAssessment": {
"questionName": "Aquatic biodiversity",
"questionID": "3kGTBsESPeYQoA8ae2Ocoy",
"questionCategoryID": "5aBe7kuYWIEoyqWCWcAEe0",
"question": "Waterways protected from nutrient runoff and stock access through fencing, buffer strips and off stream watering points",
"questionImage": "http://images.contentful.com/vkfoa0gk73be/4pGLv16BziYYSe2ageCK04/6a04041ab3344ec18fb2ecaba3bb26d5/thumb1_home.png",
"_id": "57750cf6197f0b5137d259a1",
"actions": [
{
"_id": "577512c6af3a87543932e675",
"createdAt": "2016-06-30T12:38:30.314Z",
"updatedAt": "2016-06-30T12:38:30.314Z",
"__v": 0,
"Evidence": [],
"setReminder": "",
"description": "sdsdsd",
"priority": "High",
"created": "2016-06-30T12:38:30.312Z",
"actionTitle": "sdsd"
}
],
"answer": "Relevant"
},
"locations": []
} ], "message": "", "extendedMessage": "", "timeStamp": 1467351827979 }
I see that there are many answers, I am new to mongoldb and I would like to share my answer too.
I am using aggregate function along with lookup to populate the patients.
To make it easy to read I have changed the names of the collections and fields.
Hope it's helpful.
DB:
db={
"appointmentCol": [
{
_id: ObjectId("518ee0bc9be1909012000001"),
date: ISODate("2013-05-13T22:00:00Z"),
patientId: ObjectId("518ee0bc9be1909012000001")
},
{
_id: ObjectId("518ee0bc9be1909012000002"),
date: ISODate("2013-05-13T22:00:00Z"),
patientId: ObjectId("518ee0bc9be1909012000002")
},
{
_id: ObjectId("518ee0bc9be1909012000003"),
date: ISODate("2013-05-13T22:00:00Z"),
patientId: ObjectId("518ee0bc9be1909012000003")
}
],
"patientCol": [
{
"_id": ObjectId("518ee0bc9be1909012000001"),
"name": "P1"
},
{
"_id": ObjectId("518ee0bc9be1909012000002"),
"name": "P2"
},
{
"_id": ObjectId("518ee0bc9be1909012000003"),
"name": "P3"
},
]
}
Aggregate Query using lookup:
db.appointmentCol.aggregate([
{
"$lookup": {
"from": "patientCol",
"localField": "patientId",
"foreignField": "_id",
"as": "patient"
}
}
])
Output:
[
{
"_id": ObjectId("518ee0bc9be1909012000001"),
"date": ISODate("2013-05-13T22:00:00Z"),
"patient": [
{
"_id": ObjectId("518ee0bc9be1909012000001"),
"name": "P1"
}
],
"patientId": ObjectId("518ee0bc9be1909012000001")
},
{
"_id": ObjectId("518ee0bc9be1909012000002"),
"date": ISODate("2013-05-13T22:00:00Z"),
"patient": [
{
"_id": ObjectId("518ee0bc9be1909012000002"),
"name": "P2"
}
],
"patientId": ObjectId("518ee0bc9be1909012000002")
},
{
"_id": ObjectId("518ee0bc9be1909012000003"),
"date": ISODate("2013-05-13T22:00:00Z"),
"patient": [
{
"_id": ObjectId("518ee0bc9be1909012000003"),
"name": "P3"
}
],
"patientId": ObjectId("518ee0bc9be1909012000003")
}
]
Playground:
mongoplayground.net
I used lookup instead, and it worked well. See the code snipped below.
Post.aggregate([
{
$group: {
// Each `_id` must be unique, so if there are multiple
// posts with the same category, MongoDB will increment `count`.
_id: '$category',
count: { $sum: 1 }
}
},
//from: is collection name in MongoDB, localField are primary and foreign keys in Model.
{$lookup: {from: 'categories', localField: '_id', foreignField:'_id', as: 'category'}}
]).then(categoryCount => {
console.log(categoryCount);
let json = [];
categoryCount.forEach(cat => {
console.log(json);
});