I have a processes document with a nested attachments array, I want to return get the fileName with the processes _id and attachment _id.
I have tried many options, my latest attempt still return all items from the attachments array. I only want the attachment that matches the attachment id past in.
db.getCollection('processes').find(
{$and: [ { "_id" : ObjectId("5a9455d7854cd987a40b1ba4") },
{ "attachments._id" : ObjectId("5a983da6201ba5a2302fb38f") }]},
{'attachments._id': 1, 'attachments.fileName': 1}
)
Any suggestion is greatly appreciated, thanks!
You can use $elemMatch in projection to get only one filtered subdocument from nested array:
db.getCollection('processes').find(
{ "_id" : ObjectId("5a9455d7854cd987a40b1ba4") },
{ attachments: { $elemMatch: { _id: ObjectId("5a983da6201ba5a2302fb38f") } } } )
Related
I have a large amount of data (~160M items) where a date value wasn't populated on the sub-document array fields, but was populated on the parent document. I'm very new to MongoDB and having trouble figuring out how to $set the field to match. Here's a sample of the data:
{
"_id": "5f11d4c48663f32e940696ed",
"Widgets":[{
"WidgetId":663,
"Name":"Super Widget 2.0",
"Created":null,
"LastUpdated":null
}],
"Status":3,
"LastUpdated":null,
"Created": "2018-11-09T18:22:16.000Z"
}
}
My knowledge of MongoDB is pretty limited but here's the basic aggregation I have created for part of the pipeline and where I'm struggling:
db.sample.aggregate(
[
{
"$match" : {
"Donors.$.Created" : {
"$exists" : true
}
}
},
{
"$match" : {
"Widgets.$.Created" : null
}
},
{
"$set" : {
"Widgets.$.Created" : "Created" // <- This is where I can't figure out how to define the reference to the parent "Created" field
}
}
]
);
The desired output would be:
{
"_id": "5f11d4c48663f32e940696ed",
"Widgets":[{
"WidgetId":663,
"Name":"Super Widget 2.0",
"Created":"2018-11-09T18:22:16.000Z",
"LastUpdated":null
}],
"Status":3,
"LastUpdated":null,
"Created": "2018-11-09T18:22:16.000Z"
}
}
Thanks for any assitance
Are you attempting to add the Created field to sub documents on query/aggregation? Or are you attempting to update/save the Created field on the subdocuments?
The $ is an update operator, to be used with updateMany or updateOne. Not aggregate.
https://docs.mongodb.com/manual/reference/operator/query-array/
https://docs.mongodb.com/manual/reference/operator/update-array/
If you just want to add the parents Created field to all subdocuments on query/aggregation this is all you have to do: https://mongoplayground.net/p/yHDHULCSTIz
db.collection.aggregate([
{
"$addFields": {
"Widgets.Created": "$Created"
}
}
])
If your attempting to save the parents Created field to all subdocuments:
db.sample.updateMany({"Widgets.Created" : null}, [{$set: {"Widgets.Created" : "$Created"}}])
Note: This matches any doc that has a subdocument with a null Created field and updates all the subdocuments.
Trying to query Mongo, and get 1 field of element 0, inside a document, namely emails[0].address:
Here's a sample (truncated) document structure:
{
"_id" : "dfadgfe266reh",
"emails" : [
{
"address" : "email#domain.com",
"verified" : false
}
]
}
And my query (truncated) is like this:
{
fields: {
'emails.0.address': {
address: 1
}
}
}
However, when I run this, I get an empty object array, namely emails:[{}]
But if I change the selector to 'emails.address' it will give me the actual email address -- the problem is I only want emails[0].address
What am I doing wrong?
To get the required document you need a project document with two attributes. First one, as #Veeram mentioned, slices the array and second to specify an attribute from the embedded document in the array. See code:
db.collection.find( {}, { "emails": { $slice: 1 } , "emails.address": 1} );
You can use $ in projection:
.find({"emails.address":{$exists:true}}, {"emails.$.address":1})
I am using aggregation with mongoDB now i am facing a problem here, i am trying to match my documents which are present in my input array by using $in operator. Now i want to know the index of the lement from the input array now can anyone please tell me how can i do that.
My code
var coupon_ids = ["58455a5c1f65d363bd5d2600", "58455a5c1f65d363bd5d2601","58455a5c1f65d363bd5d2602"]
couponmodel.aggregate(
{ $match : { '_id': { $in : coupons_ids }} },
/* Here i want to know index of coupon_ids element that is matched because i want to perform some operation in below code */
function(err, docs) {
if (err) {
} else {
}
});
Couponmodel Schema
var CouponSchema = new Schema({
category: {type: String},
coupon_name: {type: String}, // this is a string
});
UPDATE-
As suggested by user3124885 that aggregation is not better in performance, can anyone please tell me the performance difference between aggregation and normal query in mongodb. And which one is better ??
Update-
I read this question on SO mongodb-aggregation-match-vs-find-speed. Here the user himself commented that both take same time, also by seeing vlad-z answer i think aggregation is better. Please if anyone of you have worked on mongodb Then please tell me what are your opinion about this.
UPDATE-
I used sample json data containing 30,000 rows and tried match with aggregation v/s find query aggregation got executed in 180 ms where find query took 220ms. ALso i ran $lookup it is also taking not much than 500ms so think aggregation is bit faster than normal query. Please correct me guys if any one of you have tried using aggregation and if not then why ??
UPDATE-
I read this post where user uses below code as a replacement of $zip SERVER-20163 but i am not getting how can i solve my problem using below code. So can anybody please tell me how can i use below code to solve my issue.
{$map: {
input: {
elt1: "$array1",
elt2: "$array2"
},
in: ["$elt1", "$elt2"]
}
Now can anyone please help me, it would be really be a great favor for me.
So say we have the following in the database collection:
> db.couponmodel.find()
{ "_id" : "a" }
{ "_id" : "b" }
{ "_id" : "c" }
{ "_id" : "d" }
and we wish to search for the following ids in the collections
var coupons_ids = ["c", "a" ,"z"];
We'll then have to build up a dynamic projection state so that we can project the correct indexes, so we'll have to map each id to its corresponding index
var conditions = coupons_ids.map(function(value, index){
return { $cond: { if: { $eq: ['$_id', value] }, then: index, else: -1 } };
});
Then we can then inject this in to our aggregation pipeline
db.couponmodel.aggregate([
{ $match : { '_id' : { $in : coupons_ids } } },
{ $project: { indexes : conditions } },
{ $project: {
index : {
$filter: {
input: "$indexes", as: "indexes", cond: { $ne: [ "$$indexes", -1 ] }
}
}
}
},
{ $unwind: '$index' }
]);
Running the above will now output each _id and it's corresponding index within the coupons_ids array
{ "_id" : "a", "index" : 1 }
{ "_id" : "c", "index" : 0 }
However we can also add more items in to the pipeline at the end and reference $index to get the current matched index.
I think you could do it in a faster way simply retrieving the array and search manually. Remember that aggregation don't give you performance.
//$match,$in,$and
$match:{
$and:[
{"uniqueID":{$in:["CONV0001"]}},
{"parentID":{$in:["null"]}},
]
}
}])
Here is an example of a document from the collection I am querying
meteor:PRIMARY> db.research.findOne({_id: 'Z2zzA7dx6unkzKiSn'})
{
"_id" : "Z2zzA7dx6unkzKiSn",
"_userId" : "NtE3ANq2b2PbWSEqu",
"collaborators" : [
{
"userId" : "aTPzFad8DdFXxRrX4"
}
],
"name" : "new one",
"pending" : {
"collaborators" : [ ]
}
}
I want to find all documents within this collection with either _userId: 'aTPzFad8DdFXxRrX4' or from the collaborators array, userId: 'aTPzFad8DdFXxRrX4'
So I want to look though the collection and check if the _userId field is 'aTPzFad8DdFXxRrX4'. If not then check the collaborators array on the document and check if there is an object with userId: 'aTPzFad8DdFXxRrX4'.
Here is the query I am trying to use:
db.research.find({$or: [{_userId: 'aTPzFad8DdFXxRrX4'}, {collaborators: {$in: [{userId: 'aTPzFad8DdFXxRrX4'}]}}] })
It does not find the document and gives me a syntax error. What is my issue here? Thanks
The $in operator is basically a simplified version of $or but you really only have one argument here so you should not even need it. Use dot notation instead:
db.research.find({
'$or': [
{ '_userId': 'aTPzFad8DdFXxRrX4'},
{ 'collaborators.userId': 'aTPzFad8DdFXxRrX4'}
]
})
If you need more than one value then use $in:
db.research.find({
'$or': [
{ '_userId': 'aTPzFad8DdFXxRrX4'},
{ 'collaborators.userId': {
'$in': ['aTPzFad8DdFXxRrX4','aTPzFad8DdFXxRrX5']
}}
]
})
I am seriously baffled by mongodb's aggregate function. All I want is to find the newest document in my collection. Let's say each record has a field "created"
db.collection.aggregate({
$group: {
_id:0,
'id':{$first:"$_id"},
'max':{$max:"$created"}
}
})
yields the correct result, but I want the entire document in the result? How would I do that?
This is the structure of the document:
{
"_id" : ObjectId("52310da847cf343c8c000093"),
"created" : 1389073358,
"image" : ObjectId("52cb93dd47cf348786d63af2"),
"images" : [
ObjectId("52cb93dd47cf348786d63af2"),
ObjectId("52f67c8447cf343509d63af2")
],
"organization" : ObjectId("522949d347cf3402c3000001"),
"published" : 1392601521,
"status" : "PUBLISHED",
"tags" : [ ],
"updated" : 1392601521,
"user_id" : ObjectId("52214ce847cf344902000000")
}
In the documentation i found that the $$ROOT expression addresses this problem.
From the DOC:
http://docs.mongodb.org/manual/reference/operator/aggregation/group/#group-documents-by-author
query = [
{
'$sort': {
'created': -1
}
},
{
$group: {
'_id':null,
'max':{'$first':"$$ROOT"}
}
}
]
db.collection.aggregate(query)
db.collection.aggregate([
{
$group: {
'_id':"$_id",
'otherFields':{ $push: { fields: $ROOT } }
}
}
])
I think I figured it out. For example, I have a collection containing an array of images (or pointers). Now I want to find the document with the most images
results=[];
db.collection.aggregate([
{$unwind: "$images"},
{$group:{_id:"$_id", 'imagecount':{$sum:1}}},
{$group:{_id:"$_id",'max':{$max: "$imagecount"}}},
{$sort:{max:-1}},
{$group:{_id:0,'id':{$first:'$_id'},'max':{$first:"$max"}}}
]).result.forEach(function(d){
results.push(db.stories.findOne({_id:d.id}));
});
now the final array will contain the document with the most images. Since images is an array, I use $unwind, I then group by document id and $sum:1, pipe that into a $group that finds the max, pipe it into reverse $sort for max and $group out the first result. Finally I fetchOne the document and push it into the results array.
You should be using db.collection.find() rather than db.collection.aggregate():
db.collection.find().sort({"created":-1}).limit(1)