This question already has answers here:
convert a $lookup result to an object instead of array
(4 answers)
Closed 12 months ago.
I am currently using an aggregate lookup method from mongoose and it works:
const data = await this.messageModel.aggregate([
{
$match: { channel_id: channel_id },
},
{
$limit: limit ? limit : 1000,
},
]).lookup({
from: 'users',
localField: 'author',
foreignField: 'id',
as: 'author',
pipeline: [
{ $project: { _id: 0, password: 0, email: 0, __v: 0 } }
],
});
The data returns an array of object like this
{
"_id": "622861fe264eaed05a32bb2d",
"channel_id": "5850473746686541647",
"author": [
{
"username": "UnusualAbsurd",
"status": "Working...",
"createdAt": "2022-03-08T14:02:53.728Z",
"id": "1"
}
],
"id": "5850638795510120271",
"createdAt": "2022-03-09T08:14:54.228Z",
"attachments": [],
"content": "zazaza",
"__v": 0
}
Now the problem is, the author object that I used the lookup() method on returns as an array. How do I make it not return as an array?
You can use $unwind after lookup like this:
{$unwind: '$author'}
when i do a lookup in mongodb i enter an as field and the data is loaded into this field. But if I have an array of objects and one of the fields is a REF field then I always have the problem that the data from the lookup is always loaded into a separate field and I cannot find it with the array. How can I do a lookup that loads the data directly into the array element.
for example
i have a organisation with an array of users and there status and role in the organisation
{
_id: "60cc87da3a530000173f6d33",
"baseData": {
"name": "Organisation 1",
"email": "org#gmail.com",
"image": "",
"description": "desc",
"users": [
{
userID: "60cc87803a530000173f6d2d",
userStatus: "active" ,
userOrgRole: "Admin"
},
{
userID: "60cc87803a530000173f9h4u",
userStatus: "active" ,
userOrgRole: "User"
}
]
}
}
when i made a lookup an define the as field as baseData.users the user array are overwirte with the user data. But how i can add the data to each users array.
for example this is the result i need
{
_id: "60cc87da3a530000173f6d33",
"baseData": {
"name": "Organisation 1",
"email": "org#gmail.com",
"image": "",
"description": "desc",
"users": [
{
userID: "60cc87803a530000173f6d2d",
userStatus: "active" ,
userOrgRole: "Admin"
// userdata data from lookup for each array
},
{
userID: "60cc87803a530000173f9h4u",
userStatus: "active" ,
userOrgRole: "User"
// userdata data from lookup for each array
}
]
}
Try this way, add these stages to aggregation pipeline. It will help to add user details..
{
$unwind: {
path: "$baseData.users",
preserveNullAndEmptyArrays: true,
},
},
{
$lookup: {
from: "users", // replace with your collection name
localField: "baseData.users.userID",
foreignField: "_id",
as: "baseData.users",
},
},
{
$group: {
_id: "$_id",
baseData: {
$push: "$baseData",
},
},
},
I am creating mongodb with aggregate in which it should join two table so I have used $lookup but query returning me empty array
here is my query
return userScoringModel.aggregate([
{
"$match": {
examId: new ObjectId(req.params.examId),
user_Id: new ObjectId(req.params.userId),
subject: subject,
correctMark: {$lt: 0}
}
},
{
$lookup: {
from: "examPortalQuestions",
localField: "questionId",
foreignField: "_id",
as: "question_text"
}
},
{
"$group": {
"_id": {chapter: '$chapter'},
"questionNumbers": {$push: "$questionNo"},
"question_text": {$push: '$question_text'}
}
},
{
"$project": {
"_id": 0,
"subject": {
"name": "$_id.subject",
"chapter": "$_id.chapter",
"questionNumber": "$questionNumbers",
"question": "$question_text"
}
}
}
]).exec()
and here is output
{
"subject": {
"chapter": "NUMBER TEST AND PAIR FINDING",
"questionNumber": [
"20"
],
"question": [
[]
]
}
},
sample collection
score table:
_id, examid, userid , questionId, chapter
objectId ObjectId ObjectId ObjectId (ref:'questiontable') XYZ
objectId ObjectId ObjectId ObjectId (ref:'questiontable') qwe
Question table :
_id, question,
ObjectId what is abc?
here I am getting question array empty
can someone suggest me how to archive it
thanks in advance
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);
});